The Sunbeam ambulance, based on the 12/16 car chassis was, along with Daimler, Wolseley and Ford, one of the preferred makes of the British War Office in 1914. As the war progressed, Vauxhall, Napier, Austin and Siddley-Deasy also supplied large numbers of ambulances.

In November 1914, No.1 Motor Ambulance Convoy commented that Sunbeam ambulances were good cars but lacked ground clearance. This problem was easily solved by fitting spacers between the axles and road springs. At the same time, the Inspector-General Communications reported to the War Office that Sunbeams and Fords were the best ambulances. With vehicles in short supply, American Buicks began to be supplied through the British Red Cross Society and these made exclusive use of Sunbeam fittings.

A census conducted on behalf of the Director of Transport in September 1915, offers an explanation as to the War office preference for Sunbeams. The percentage of breakdowns was identified as Daimler 16.7%, Singer 4.9%, Vauxhall 5.5%, Wolseley 5.4% and Sunbeams best of all at 3.7%.

In May 1916 the Ministry of Munitions awarded a contract to the Rover Company to manufacture Sunbeams. This contract formalised the arrangements made in December 1915 when the Rover Co had been requisitioned to manufacture Sunbeam ambulances and spare parts. This had been necessary as Sunbeam were unable to keep up with the demands made of them.

The reason that Sunbeam could not maintain supply was that the company was increasingly employed by the Admiralty building aero engines. Both the Royal Naval Air Service and the Royal Flying Corps remained adamant that their ‘flying machines’ had to be built with the highest quality components. Sunbeam engineering and quality was greatly admired by the Admiralty and therefore the production of ambulances and spare parts had to take second place. There appears to have been an argument that engine failure while on the road simply resulted in gently rolling to a stop, whereas engine failure while 10,000 feet above the ground was an altogether more serious affair.

On 22 May 1916, the Director of Army Contracts informed the Director of Naval Contracts that the Admiralty’s request that Sunbeam concentrate solely on manufacture of aero engines had been approved. The War Office had lost its preferred supplier of ambulances to the seniority of the Admiralty.

With the War Office preferring the Sunbeam, and Rover not having a suitable model, all the machine tools and equipment was transferred from the Sunbeam factory in Wolverhampton to the Rover factory in Coventry. A similar arrangement was also in place with the Maudslay lorry company for Rover to build lorries of Maudslay design, allowing Maudslay to build munitions.

This transfer of one factory to another caused great delays and despite the contract for seven ambulances per week, Rover were unable to supply a single one in the first six months. Despite requests by the War Office for the Admiralty relinquish some of Sunbeam’s capacity to build ambulances, the Admiralty refused, arguing that their aero engines were more urgently needed than ambulances for the army.

With the supply of spare parts non-existent and desperately needed in France, the Admiralty finally relented in December 1916 and allowed the production of spare parts to resume at Sunbeam provided no more than ten men were employed. This was increased to fifty in April 1917 as the spare parts supply had reached crisis point.

By the end of the war there were around 3,000 Sunbeam ambulances in France, although most of them were actually built by Rover.