Author: Zoe Tolman, Assistant Archivist

Most of the modifications we’ve looked at so far have been… explosive, to say the least. Today however we’re going back along the lines of the DD Tank, to look at something which proved most useful when crossing bodies of water.

The CDL, or Canal Defence Light, was designed for night missions. Essentially a very powerful searchlight mounted upon a Matilda, and later the Grant tank, the CDL had multiple potential uses. It could provide movement light for allied forces, pick out and illuminate the enemy for accurate aimed fire while allied troops remained hidden (with the exception of the CDL itself of course) and even dazzle and confuse the enemy. The Grant was considered a far better design as the light did not replace the main armament as it did on the Matilda.

Model of a Matilda CDL. E:95.1365.02.

In practice, this latter option did not work quite as hoped. The light had a shutter which could be used to make it flicker, reducing the enemy’s ability to pinpoint the source of the light and also supposedly stopping them from adapting to either light or darkness. While this could apparently work, human eyes are unfortunately very clever and most people either recovered from any sudden blinding or were not affected to being with. Blue or amber filters were also designed for the CDL which, when combined from two tanks, would still produce white light on the target. The differing shades would supposedly impact how far away the light sources appeared even when next to each other. Despite these designs, the CDL still however drew enough fire to be "intensely disliked by troops in their immediate vicinity".

The CDL was considered a secret design and only a handful of units ever operated them. One of these was 35 Tank Brigade, which was based around Penarth, Wales for the security of its training, and joined 79th Armoured Division in 1943. This also had a specialist REME section for the repair and maintenance of the CDL equipment attached to the standard tank brigade workshop. In April 1944 however, 1 Tank Brigade returned from the Middle East and also joined the division. Only one CDL brigade was required so they kept 1 Tank Bde and merged parts of 35 Tank Bde into it to bring it up to full strength, and the same happened with their workshops. More intensive training then took place at Linney Head, still in Wales.

Although training took place with the other brigades in 79th Armoured Div, showing how the various modified vehicles could best work together, the CDL were not used in the landings at Normandy, nor in the break out from the bridgehead. In fact, by the time of the operations between Ghent and Antwerp, there was "little prospect of there being a job for them". The decision was made to instead focus on other vehicles with one regiment being converted into a Buffalo one. 1 Tank Bde Wksp was therefore moved from Tilley-sur-Seules where "it had done practically no work at all" to Sas-van-Gent where they began work overhauling one Buffalo regiment and refitting another.

Despite this, the CDL did have an important role to play. 49 Royal Tank Regiment, who had been part of 1 Tank Bde, reformed a squadron outfitted with the Grant CDLs in preparation for the Rhine crossings. Positioned upstream of the crossing areas for both 12 and 30 corps, they not only provided movement light for the Buffaloes and others crossing but also illuminated and opened fire on any suspicious objects in the water. These had the potential to be enemy divers, floating mines, even miniature submarines, as well as simply obstacles. The CDLs are noted as having destroyed many floating objects, ‘35 of which blew up with a loud bang’, which could otherwise have impeded or damaged the men and vehicles crossing.

Even after the operation, the CDLs continued to prove useful in this role. They maintained a night watch on the crossing places and destroyed any further floating mines or attempts at sabotage. As such, 49 RTR were requested with their CDLs for the crossing of the Elbe as well. ‘A’ section of 30 Bde Wksps, with reinforcements of 40 men from 827 Armoured Troops Wksps, undertook a complete overhaul of the CDL in just three weeks to get them ready for this.

The CDL seems to have suffered from its own secrecy. Used in its most basic sense, it provided a great deal of support to specific operations, but because commanders were either unfamiliar with its tactical uses (or unaware of its existence in general), it was never really applied in any more complicated scenarios. Furthermore, while it could be argued that standard searchlights could have aided the river crossings just as much as the CDL, the amount of fire they came under, including heavy artillery fire at times, means the searchlight modification of an Armoured Fighting Vehicle (AFV) was in fact a far more suitable option for these cases.

---

Article sources include: E:08.0296.03 The History of 79 Armd Division, E:05.0177.05 Monograph on Design and Development of Wading Equipment for Fighting Vehicles, “79th Armoured Division : Hobo’s Funnies” by Nigel Duncan, and “Study No 52 : Armored Special Equipment” by The General Board, United States Forces, European Theater.

Published in The Craftsman, March 2025.