Flashing light signalling includes the use of searchlights, yardarm blinkers and signal lanterns employing Morse code, special characters and procedure. Directional flashing light is the term applied to the transmission of signals by a narrow beam of light. Non-directional flashing light is the term applied to the transmission of signals in all directions.

Don Wagner (USN, Ret'd) provides this introduction to Light Signalling. "On RCN or RN naval vessels, the directional signal projector was either a 10-inch Signal Projector or a 20-inch Signal Projector. In the U.S. Navy, they also came in two sizes. The 12-inch signal/search light used an incandescent bulb which could also be trained and elevated. There were also 24-inch carbon arc signal/search lights. Both of these lights were equipped with a handle on each side of the barrel (for left or right handed operators to send visual (light) Morse code. The 12-inch range was normally limited to about 14 miles or the horizon. The 24-inch carbon arc was much more brilliant and the signals (at night) could be bounced off the cloud cover and around the curvature of the earth. It has been told in visual communicators circles that a Morse signal sent by light has been confirmed (by radar) to have been sent up to a distance of two ships 80 miles apart!"


Non-Directional light signaling was accomplish by means of yardarm blinkers. The blinkers were operated by telegraph keys fitted on a ship's flag or signal deck. Some vessels also carried infrared blinkers. During WWII,  RCN ships were fitted with "fighting lights".  One e-mail source on the web made reference to the fact that fighting lights were used to send emergency messages on a broadcast  basis to a group of vessels immediately preceding or during action. This use of coded visual communication maintained security and could be construed as a form of visual IFF.

With directional light, the receiver would send a short flash on receipt of each word. With non-directional signalling this was not possible. Obviously the sender could not watch all the ships at once to see if they received the word just sent. It was assumed that the entire message was received otherwise any (receiving) signalman could request a repetition. During routine operations, there were night exercises in which the yardarm or masthead lights were used to send Morse flashing exercises to the ships in company.

In the USN, infrared signalling was known in visual communications circles as "Nancy Hanks". (Nancy Hanks was the maiden name of President Abraham Lincoln's mother). An infrared viewer was necessary to view infrared transmissions. In the USN, a Nancy viewer scope was also used to check for "light leaks" during periods of darken ship. Very often it picked up the glow of light from a "leaking" scuttle or someone having a smoke on the weather decks. Infrared viewing scopes were quite amazing in that you could even turn them on a dim star on a clear night and see that star quite clearly! In the RCN, these lights were referred to as "Nancy".

Don Ross, a former Visual Signaller in the RCN comments on Nancy.  "When an infrared signal was about to sent, the radio code words were Nancy Hanks.  This was sent a few minutes in advance so the signalmen could get the infrared reading device out of storage and be ready to read the Morse code. We used it in training quite a few times, but the only time I ever used it for real signalling was on a trip into the Baltic Sea. We were being shadowed by a squadron of Russian (destroyer like) ships.  St. Laurent's Captain (Senior Officer) used infrared to signal course and speed changes".

Signalling lights aboard HMCS HAIDA. 1- Truck lights for aircraft warning and anti-submarine action. 2 - Masthead Flashing Lanterns. 3 - Yardarm Flashing Lanterns. 4 - Fighting Lights.
5 - Infrared lights.  (Photo by Jerry Proc)
This is a partial schematic diagram of the flashing light system. Both port and starboard light sets ( ie fighting, masthead and yardarm) were connected in parallel and keyed as a group except for the infrared lamps which were keyed with separate Morse keys. The NUC lights are described elsewhere in this document. (Image courtesy RCN) 
In 2007 this flashing light control station aboard HMCS HAIDA was restored after being under a metal cover for several decades. In addition, three other similiar stations could also control the flashing lights. One identical pair was on either side of the bridge and slightly aft. The other pair of stations were on the port and starboard sides of the flag deck. Normally a curved, hinged metal cover would protect the keys from the elements. A typical  signalling speed for flashing lights would be around 13 wpm. (Photo by Jerry Proc)
Close-up of the flashing masthead lights attached to the 293 platform. The truck lights atop the shade cannot be seen from this angle.    (Photo by Jerry Proc)
Two infrared lights are fitted on each side of the lattice mast just below the yardarm.  (Photo by Jerry Proc)
Close-up of an infrared lamp. Keith Kennedy also confirms that infrared signalling was referred to as "Nancy" in the RCN. Sometimes a reddish coloured infrared filter would be placed over the 10 inch signal projector for infrared signalling but it resulted in a reduction in the size of the beam. Infrared signalling was sometimes referred to as "dark light" signalling. (Photo by Jerry Proc)
A close-up of the infrared light control key. The key is shown with its protective cover in the closed position. (Photo by Jerry Proc)


Most ships used 10 inch signal projectors but on smaller vessels, hand-held Aldis lamps were used. Larger ships like destroyers also had two 20" SP's on mountings either side of the bridge but at a slightly lower level. SP's were used to communicate with other ships in Morse code and were also known as Signalling Lanterns in the RCN.


The 10" signal projector operates with a light beam divergence of six degrees and 1 million candlepower output. In bright sunlight, a range of 10 miles can be expected. For night signalling the projector's light output can be attenuated by the use of filters which either lessen the brilliancy or convert the light to infra-red. This projector is still in use by the Canadian Navy in 2007 and  is carried on Iroquois Class, Kingston class and a couple of Halifax class frigates but not HMCS Toronto.

With directional signalling,  the operator sends at the speed of the slowest reader. There is an acknowledgment flash from the reader after every word. Repetition of words is quite common.  The NATO standard sending speed remains at 8 WPM.

This 10 inch signal projector on HMCS HAIDA's starboard size uses a 1000 watt filament-type lamp. It does not use a blower motor to exhaust hot air.  (Photo by Jerry Proc)

Nameplate data: Pattern 3860A; Serial 5676; Year: 1944; Made by: General Electric, Toronto. It is not known if this particular projector was original to the ship since there was little chance that Vickers-Armstrong (HAIDA's builder) would use an overseas subcontractor during wartime. A 1944 date might suggest that the projector was replaced during a 1944 Canadian refit or even later. 

Radio collector Richard Dillman is demonstrating a signal projector aboard the S.S. Lane Victory. The size of the projector is believed to be around 10 inches. (Photo via  Richard Dillman) 

Principal parts of a 10 inch signal projector. (Images courtesy RCN)

The 12 inch signal projector, the same type as used by the United States Navy, was introduced into the Canadian Navy fleet in approximately 1981. Confirmation has been received that  HMCS ALGONQUIN 283 had them by  January 1982. In 2007, the Canadian Navy  fleet has approximately a 50/50 mixture of 10 and 12 inch signal projectors.
The primary signal projector on Halifax and Iroquois classes is the 12” size.


 These projectors used a carbon arc light source. Each pair of carbon rods lasts approximately 50 minutes. When used as a searchlight, the lamp is focused so the beam is narrow, having a divergence of 2.6 degrees and a minimum brilliance of 45 million candlepower.

When used as a signalling projector, the beam's divergence is increased to 4.5 degrees thus giving a brilliance level in the order of 10 million candlepower. A broader beam was more desirable for directional signalling because it shows up on the horizon as a "splash" of light which is much easier to see than the pinpoint of light characteristic of a searchlight beam.

Banging one's hand on the shutter handle would not permit faster signalling. The projector had  be operated with light pressure of the fingers. Special attention had be paid to the spacing of the dots and dashes to ensure that the Morse code was readable. While signalling, one eye had to be constantly in the sight so as to compensate for ship's own motion and maintain a visual lock on the other ship.

Twenty inch signal projectors used by the USN used carbon rods about 12" to 15" long and had a diameter about the size of a pencil.

The use of the 20 inch signal projector was phased out by the Canadian Navy around 1985. It is believed that HMCS Athabaskan 282 was the last ship to use one.

Principal parts of a 20 inch signal projector. (Image courtesy RCN)
Starboard side 20 inch signal projector aboard HMCS HAIDA Type 170A Mk IV. It could also double as a searchlight.  (Photo by Jerry Proc) 

Nameplate Data: Pattern 170A; Serial 1488; Year 1943; Made by Metropolitan Vickers. [1] 

This photo illustrates the internal components of the 20 inch signal projector. (Photo by Jerry Proc) 

NAMEPLATE DATA : 20 inch Lamp Mark IV; Volts 67 Amps 85; Pattern  No 173; Made by Canadian General Electric; Serial No 1347 Date 1945. 

Closeup of the carbon arc elements which consume 5700 watts of power in this model. After the arc is flashed up, an internal motor rotates the carbon rods slowly and at the same time a ratchet mechanism pushes them forward to maintain a constant gap as the heat consumes the carbon. Without a drive mechanism for the carbon rods,  it would be an impossibility for a signalman to keep the arc lit, train and elevate the light and operate the shutters while a ship was rolling and pitching! (Photo by Jerry Proc) 
This 20 inch signal projector, fitted on HAIDA's port side, illustrates the shutter detail. It is not known if this projector was original to the ship. It's missing the blower assembly. No nameplate data is available at this time. Power from the ship's 220 volt DC mains was applied to three resister boxes connected in series which would drop the voltage down to a safer level  - around 67 volts. The projector was energized with a three pole connect/disconnect switch. As of 2007, signal  projectors are still used by most of the world's navies including the Royal Navy and the United States Navy. (Photo by Jerry Proc)

Xenon search lights are now used for (night) Man Overboard situations and can also be used to illuminate a vessel being hailed. These were not available in the 1960's.


The RN first started using Aldis lanterns  in the 1800's and the rest of the navies adapted this form of  flashing light using Morse code. Royal Navy, RCN and USN versions of the Aldis were slightly different whereby the USN models used a shutter to key the light beam while those in the RCN and RN used a tilting mirror.

Those used in the RCN  were hand-held projectors about 4 inches in diameter, which had a pistol grip and a trigger to control the light. Aldis lamps used either 12 volt or 36 volt bulbs to send messages in Morse code. When using the ship's low power mains in DC fitted ships and when using a portable battery, 12 volt lamps were used. The 36 volt bulbs were used in AC fitted ships. Along the top, there was a sight which was used to aim the lantern.  The lantern was usually rested on the crook of one elbow, held shoulder high while the other two triggers were operated by the opposite hand. When using portable wet cell battery, the Signalman had to ensure it was kept charged when not in use.

The pistol grip is fitted with two triggers. The lower trigger turns on the lamp and must remain depressed for the duration of the message while the upper trigger tilts the mirror. When the lantern is accurately trained on the receiving station and even if the lamp is on, nothing will be seen until the beam is raised by pressing the upper trigger. Releasing the upper trigger drops the beam thus producing breaks between the dots and dashes of the Morse code characters.  During darkness, colored filters could be attached to the lantern to reduce the lamp's  brilliance.

The 5 inch Aldis lantern combines the features of the 4 inch Aldis lantern and the Intermediate Lanterns. It uses the same power supply but produces 150,000 candlepower. Coloured shades can be secured to the front glass to reduce the brilliancy for night signalling. HMCS HAIDA's electrical drawing shows places for two 6 inch Aldis lanterns both running at 22 VDC, however the Signalman Trade Group 1 Manual does not mention anything about 6 inch Aldis lanterns.

Don Wagner details USN usage of the Aldis. "In the USN, the Aldis lamp had a 6 inch diameter barrel with a pistol grip and a "trigger" to operate the lamp shutters. It was used by submarines on the surface and maritime Navy patrol aircraft to communicate with destroyers engaged in depth charging enemy subs. The lamp could be operated by plugging it into the ships power mains or into a portable battery pack. The Aldis was also used in small craft."

The Royal Navy phased out the use of Aldis lamps in 1997, although by that time they were largely ceremonial. Other modern forces have followed suit as technological advances in digital communications have made the device obsolete. HMCS Toronto still carries five Aldis lamps on the bridge for backup purposes.

Above and below: 4 inch Aldis lantern, pattern S5110E. Made by Sutton-Horsley Co. Ltd, of Toronto Ontario. This one was last used on HMCS Labrador. Since there was no battery compartment in the carrying case and the lamp has a long power cord, it is believed it was powered from the ship's low voltage power mains. Five inch Aldis lamps produce 150,000 candlepower.  (Photo by Jerry Proc) 

Aldis Lantern, 5 inch - Principal parts. (Image courtesy RCN)
5 inch Aldis Lantern  - Cutaway side view. (Image courtesy RCN)

WRENS practicing with the Aldis lamp likely at the training facility at St. Hyacinth. (DND Imaging Centre photo # 209639-1)

The Intermediate Lantern produces 2 to 2000 candlepower depending upon the position of its control switch. When connected to a power source, the lamp illuminates continuously although this is not apparent unless the trigger is pressed. A sleeve of metal, which completely covers the lamp is attached to the trigger. Morse code is generated by covering and uncovering the lamp using the trigger. Since the lamp is normally covered by the metal sleeve, it is also very easy to forget that the light is on so the operator might store it while still switched on. Apart from potential damage caused by overheating and the attendant fire hazard, leaving the lamp switched on for extended periods of time required more frequent changes of the bulb.

A modernized version of this type of lantern is carried by HMC ships in 2007. HMCS Toronto still has two Intermediate Lanterns on the bridge for backup purposes.


This device uses an Edison Mazda 1W 2V bulb, Patt 1039A and powered by a rechargeable battery in a box slung beneath the instrument. It was smaller than the Aldis Lamp and used for night-time convoy identification, hence the reason for using a low power (1 watt) bulb. Internally, it has sockets for 2 bulbs  (one to hold a spare). The operator can select one of five coloured lenses – blue,/ red,  green, white or clear. In the RCN, it was used  at close quarters but night time only.

AP1038  side view. The lens is on the left side (Photo by Douglas Moore)
AP1038 internal view. The spare bulb socket is at the top centre.   (Photo by Douglas Moore)
AP1038 – Front view of lenses. (Courtesy
AP1038 operator instruction plate.  (Photo by Douglas Moore)

Intermediate Lantern - Front view. The black cylindrical object in front of the mirror is the shutter.  It moves forward when the trigger is engaged thus allowing light to escape. (Photo by Jerry Proc)
Intermediate Lantern - Side view. Admiralty Pattern Number AP2174.  (Photo by Jerry Proc)
Intermediate Lantern - Rear View. The control dial selected the power source (mains or battery) and the light intensity for each power source. (Photo by Jerry Proc)
An Intermediate Lantern disassembled into its principle parts. (Photo courtesy RCN)
The Daylight Signalling lantern (DSL) was fitted in cruisers (ie HMC's Ontario and Uganda) and larger ships and mounted in pairs on the side of the mast, bridge or funnel. It was used for non-directional signalling during daylight. DSL had a horizontal divergence of 200 degrees and a vertical divergence of +/- 10 degrees. It's 25,000 candlepower output gave it a range of several miles.

Morse code was produced by the keying of an electric shutter fitted inside the lantern. The shutter could be keyed from several locations on the bridge or flag deck of the ship.


Not Under Command  Lights

NUC (Note 2)  lights are two red lights joined together by a six foot length of wire rope or halyard.  The condition means that the ship cannot obey the "rules of the road" and all other ships must give her the right of way. These lights were hoisted on a signal halyard during the hours of darkness to indicate a breakdown or man overboard. They had to be ready for instant use between sunset and sunrise. During daytime, two black balls would be used to signal a NUC condition.

The Signalman of the Watch would test the lights to ensure they were working properly then he would hoist them on the yardarm. When in position, the Officer of  The Watch was informed. When required,  they were turned on and left on to indicate a breakdown or flashed to indicate man overboard.

Halifax class ships have red and white NUC lights built into the mast to inform other ships of any of the following states: NUC, RAM  (Restricted in Ability to Manoeuver), Man Overboard (MOB) or prosecuting a sonar contact. These light are not optional as they are mandated by the International Regulations for Preventing Collisions at sea (COL REGS).

NUC lights. (Image courtesy RCN)


Two black balls, separated by tackline could be used by day to indicate that a ship is Not Under Command.  By night it was two vertical red lights. A vessel at anchor would hoist one black ball on the yardarm  corresponding to the side on which her anchor is down.  The anchor ball is hoisted when the anchor is dropped and is hauled down when the anchor is aweigh. Light on top of the jackstaff denotes anchored at night plus the running lights would be off.

Diamonds are also carried so a ship can inform other ships of its status. The pattern Blackball -Diamond- Blackball means - "Restricted in ability to maneuver".

Theree blackballs means "I've run aground". Black balls are still carried aboard HMC ships in 2007 since the carrying of shapes is also mandated by COL REGS.

This is a canvas black ball, the type used by the RCN in the 1960's. This example aboard HMCS HAIDA is in a near petrified state after having been stored outdoors for several decades until it was discovered in 2002. Handled with care for the photo shoot, it was not forced to deploy to its fully open position. Normally the top would be peaked like the bottom. (Photo by Jerry Proc)
Here's how two black balls looked when secured with regulation length tackline. The bottom one is in a fairly deteriorated state. (Photo by Jerry Proc)

visual_black_ball_comm.jpg /visual_diamond.jpg
Commercial marine black ball. (Image courtesy Thomas Gunn Services)  Commercial marine diamond. (Image courtesy Thomas Gunn Services) 
HMCS HAIDA:  Situated on the bridge rail between segments of the torpedo aiming/firing controls is a short pin used for holding a signalman's board on which signals were clipped. The captain and the officer of the watch could then read it at their convenience while the signalman read another flashing light message. (Photo by Jerry Proc)

The choice of which lantern or projector to use was generally left to the operator's discretion. His choice would have been based on several factors some of which are: distance, amount of daylight, sea state, presence of other ships and background. Signalling at dusk and dawn was kept to a minimum as this is a critical period when the ship's position could easily be betrayed to an adversary by the display of lights. There was a requirement to use a minimum amount of light for message transmission, hence the operator may have to change from one piece of equipment to another as circumstances dictate.

It was also possible to reduce the brilliancy of a lantern after communications were established. If the light output from a sending ship was too brilliant, the receiving ship would sent a series of 'D' characters until the sending ship reduced the brilliancy of its light.

The special abbreviation OL was used to tell the receiving station to show a steady dim light. This was done at night when using small directional flashing lanterns which must be accurately trained in order to be seen. If reception became difficult owing to a badly aimed or poor light, the receiving station was expected to flash a series of 'W' characters whereupon the sender was expected to direct a steady beam of light until the letter 'K' (meaning proceed) was received. For signalling to one station only, a directional lantern was generally used.

Directional procedure is a method which requires each group (word, prosign, code group, or operating signal to be acknowledged by a flash from the receiving station before the next group is transmitted. Should the receiving station miss a group, it was repeated by the transmitter as often as necessary until a flash was received.

Now... fast forward to 2007 and a comment from a current serving NAV COMM describing his Halifax class ship.  "We have two yardarm blinkers, one at each end. Keying boxes for the light are found on the bridge and on the bridge wings. Yardarm blinkers are used for Non-directional light sending of a large message. Non-directional protocol is complicated and few if any navies use them as a method of sending signals. Generally, messages are send via teletype or satellite. Visual Comms is used for short tactical signals or operator to operator short messages. Directional signalling with lanterns is far superior and less prone to error".


The primary small signaling lantern in the Canadian Navy circa 2007 is the Wiska Richtblinker RBL available from Rainer Förtig Elektronik . It is a plastic, battery operated signaling gun with interchangeable colour filters. In the Canadian Navy, it's referred to as the Wiska lantern.

Powered by battery, the Wiska Richtblinker RBL has a 70 mm wide lens and a focal length of 30 mm. It uses a 4 V, 0.75 amp projection lamp and weights about 1.0 kg. (Photo courtesy Rainer Förtig Elektronik)


 John MacFarlane recalls his training at Cornwallis. " I remember that Morse visual training was conducted with a lamp for the first year UNTD cadets at Cornwallis. A projector was mounted on the outside of the second floor of the H-hut which housed the Gunroom and classrooms. Cadets would stand in the courtyard – one with a clipboard with back turned to the lamp and the other softly calling out the letters or numbers which were duly recorded. All cadets had to qualify regardless of the number of attempts necessary to pass. The speed was probably 5 wpm – which was easy for me but perplexed many of my colleagues.

Once I passed the test on the first try,  I was delegated to transcribe for all the other testers. Typically some of them ‘just didn’t get it’ so I would stand so that I could see the lamp reflected in a window. Of course the copy is same either way so I simply recorded the message and passed numerous shipmates who would never have passed otherwise. That was good for rounds of beer in the Gunroom and elevated my popularity. Eventually the instructors began to suspect me – and I was forced to move to another location  which put me out of business. I know, I should be ashamed but it still brings a chuckle!

We were not required to send – but I was employed in Gate Vessels as a Cadet visual communicator and got practice at sea sending and receiving which I enjoyed thoroughly. The lamp however hobbled me in learning to send CW on radio and it took some time to “forget” the visual decoding mental process! In our Second Year training, we did no more visual signalling. It was all voice procedure and fleet manoeuvres which was not as much fun".


[1] Metropolitan-Vickers, Metrovick, or Metrovicks, was a British heavy electrical engineering company of the early-to-mid 20th century formerly known as British Westinghouse. Highly diversified, they were particularly well known for their industrial electrical equipment such as generators, steam turbines, switchgear, transformers, electronics and railway traction equipment.

[2] Rule 3 of the Colregs (International Regulations for the Prevention of Collisions at Sea) provides this definition for a vessel not under command:  The term "vessel not under command" means a vessel which through some exceptional circumstance, is unable to maneuver as required by these Rules and is therefore unable to keep out of the way of another vessel.


Please refer to the Morsemad web page  which features visual light signalling.

Contributors and Credits:

1) James McAlister <themcalisters(at)>
2) Spud Roscoe <spudroscoe(at)>
3) Douglas Moore, Cornwallis Museum <cornwallismuseum(at)>
4) HMCS HAIDA Staff  Resource Manual 2003
5) Don Wagner <navwags(at)>
6) Morsemad web page
7) Jim Brewer <snack.235(at)>
10) Richard Dillman  <ddillman(at)>
11) Signalman Trade Group One Manual BRCN 3038(63). Published by RCN, 1960; revised 1963.
12) PO1 JR Stroud, Senior Nav Comm, HMCS Toronto <stroud.r(at)>
13) CPO2 Derrick Shillington. HMCS Toronto Combat /Training Chief   <shillington.c2(at)
14) Thomas Gunn Navigation Services
15) Robert Willson RCN (Ret'd) <rawillson(at)>
16) Richtblinker RBL image
17) Elsa Lessard  <elsal(at)>
18) John MacFarlane <John.MacFarlane(at)>
19) Don Ross <ddwross213(at)>

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Nov 13/13