British 13pdr AA Gun on Thornycroft J-Type Lorry
or on Daimler Mk.3 Lorry
Author: P Kempf, with a plan by Ken Musgrave, photos by Knut Erik Hagen and a video by PDA. Edited: P Radley

The huge impact aviation had on warfare, came as a surprise for many in 1914, not only leading to a massive expansion of the air arms, but also making the need for anti-aircraft artillery clear to all involved. Many more or less improvised solutions came into being on all sides of the front lines. And in many cases these guns were motorized, in order to make their tactical use as flexible as possible. One of these early improvisations can be seen here, in two guises: the British 13pdr AA Gun mounted on either a Thornycroft J-Type Lorry, or on the Daimler Mk.3 Lorry.

The 13-pdr AA gun on the Daimler Mk. 3 Lorry is shown in the excellent plan below by Ken Musgrave. (Any commercial use of this plan must be cleared with Mr Musgrave first.)

13pdr AA 1

The photo below shows the 13pdr mounted on the Daimler Mk.3.

13pdr AA 2

The firm of John Thornycroft Ltd. of Basingstoke had a long history of producing vehicles to meet military requirements and it was not surprising that Thornycroft's J Type lorry should come out best in the 1913 and 1914 War Office subsidy trials. Not only did it lead the field in most of the trials runs, but it was also the lightest vehicle competing in the 3-ton Class A. The prototype vehicle was designed in 1912 specifically to qualify for the newly announced subsidy scheme. It took part in the 1913 trials and was exhibited at the Commercial Motor Show, Olympia, the following July. The wheelbase of the J Type was 13 ft 2 in., and the width was 7 ft 2.5 in. The four-cylinder side-valve engine developed 40 h.p. In all respects the vehicle conformed to the War Office subsidy requirements; it weighed 3.25 tons (less its body), and had a top speed of 14.5 mph. More than 5,000 J Types were supplied to the British Army in the years 1914-18 and this vehicle won a great reputation on all fronts. The Thornycrofts were chosen for the more exacting special-purpose roles and those most associated with the J Type were the mobile workshops and the mobile anti-aircraft guns. The vehicle below shows the latter configuration with 3-inch A.A. gun, one of the best known vehicle types of the First World War. The Germans had designed this sort of vehicle many years earlier, but in the British Army the mobile A.A. gun was very much a last-minute improvisation produced in 1915.

13pdr AA 3 13pdr AA 4 13pdr AA 5

The mobile workshop Thornycroft was another very important type and had a van-like body with drop sides which opened out to form a working platform. Inside the body a lathe, anvil, work bench, drilling machine, grinding machine, and small auxiliary petrol engine driving a generator were the usual fittings, though equipment was changed for special functions on some vehicles. The mobile workshop companies carried out all minor running repairs (and not a few major repairs) to vehicles and guns behind the front lines. Thornycrofts served on all fronts with the British Army, and the J Type remained in production as a commercial vehicle until 1926. Early J Types had wheels with cast spokes, but these were soon changed for pressed-steel disc type.

Knut Erik Hagen took the photos, below, that show the Thornycroft J Type and 13pdr AA gun that is on display in The Imperial War Museum in Duxford, England.

13pdr AA 6 13pdr AA 7 13pdr AA 8
13pdr AA 9 13pdr AA 10

The gun used was a 13pdr field gun (either a Mk I or II, as used by the Royal Horse Artillery) removed from its normal field carriage and fitted to a rotating pedestal mount, whereupon it became '13pdr Mark III on Mounting Anit-Aircraft Mark I'. A retaining catch was fitted under the breech to hold the round in place when loading the gun at high angle. However, soon the need for a more powerful AA gun arose. At first the 18pdr was used in the same role as the 13pdr, but this was a failure ballistically speaking, so instead it was decided to use the 18pdr, but to reline it to a calibre of 76mm. This enabled it to 'accept a 13pdr shell fired from a necked-down 18pdr case' (Clarke & Delf, 2004). This proved a very successful solution, and this gun, the 13pdr 9cwt Mk 1 AA gun became the most common of all British Anti-Aircraft weapons during WW1, and served into the 1920s. The muzzle velocity of this gun was 655m/sec, giving it an effective ceiling of some 5,790 metres.

This video comes courtesy of PDA:

The gun was used in conjunction with a visual rangefinder carried in an accompanying vehicle and set up in a convenient position alongside the emplaced gun carrier. Jacks on the chassis steadied the vehicle when the gun was fired. The usual gun section was equipped with two Thornycroft gun-carrier lorries, each supported by two 3-ton lorries which carried the gun crew, the rangefinder, and ammunition.

13pdr AA 11 13pdr AA 12 13pdr AA 13


D Clarke & B Delf, British Artillery 1914-19, Field Army Artillery, 2004. Osprey Publishing Ltd, England.

How to model this vehicle

Reviresco makes a 40 part 1/72 kit in white metal, that includes a driver and 5 gun crew.