The War Office introduced the subsidy scheme to ensure that lorries would be rapidly available for military use in time of national emergency, and the scheme was set up before WW1 in the expectation of the conflict. However, the scheme failed to yield the required number of lorries when war broke out, and the War Department had to impress numbers of civilian vehicles to meet its needs. A Thornycroft document issued in December 1924, some of which is quoted verbatim below, explains how the subsidy scheme worked relative to the A1 chassis.
"After very severe tests of the Thornycroft Subsidy Type A1 chassis by the War Department (which incidentally resulted in an order being placed by the War Department for a fleet of these vehicles) we have been officially informed that this chassis has been accepted for enrolment under the Subsidy Scheme.
"The following are brief particulars of the War Department Scheme for Subsidising Thornycroft Subsidy Type A1 chassis and vehicles.
"Full official particulars will be supplied on request.
"War Department Subsidy A1 Thornycroft chassis only or vehicles with any type of body will be accepted for enrolment for a period of three years, ensuring the payment to owners of £120 per chassis or vehicle which is paid in advance in six half-yearly instalments of £20, subject to half-yearly inspection. The half-yearly inspection is welcomed by many owners and more often than not takes the form of friendly advice enabling the best service to be obtained.
"Enrolment entitles the War Department to purchase the chassis or vehicles in case of a national emergency only, involving the calling of the Army Reserve, at a specially favourable price to the owner, fixed by agreement on enrolment.
"All Thornycroft Subsidy Type A1 chassis are eligible for enrolment no matter what type of body is fitted. If the body is unsuitable for War Department purposes it is not included in the agreed purchase price and is removed and remains the property of the owner should the chassis be purchased by the War Department.
"Thus the purchaser can choose any type of body which suits him best; it is not necessary to have the War Department or any special type of body.
"Any British tyres which we list may be fitted; we supply Super-Cushion, N.A.P. or Dunlop pneumatics… etc".
Notes on the above: