During World War 1, the company returned to arms manufacture and greatly expanded its operations. At the peak of the war, the Group factories were employing approximately 20000 people. BSA produced rifles, Lewis guns, shells, motorcycles and other vehicles for the war effort.
After the armistice, it was decided to put the Company’s three main activities under separate management, and so three new subsidiaries were formed, these were BSA Cycles, BSA Guns and BSA Tools.
In 1931 the Lanchester Motor Company was acquired and production of their cars transferred to Daimler's Coventry works.
126,000 BSA M20 motorcycles were supplied to the armed forces, from 1937 (and later until 1950) plus military bicycles including the folding paratrooper bicycle. At the same time, the Daimler concern was producing armoured cars.
In 1960 Daimler was sold off to Jaguar.
The BSA bicycle division, BSA Cycles Ltd., was sold to Raleigh in 1956. Bicycles bearing the BSA name are currently manufactured and distributed within India by TI Cycles of India.
The final range was just four models: Gold Star 500, 650 Thunderbolt/Lightning and the 750 cc Rocket Three.
Out of the ashes of receivership, the NVT Motorcycles Ltd company which owned the rights to the BSA marque, was bought-out by the management and renamed the BSA Company.
In 1991, the BSA (motorcycle) Company merged with Andover Norton International Ltd., to form a new BSA Group, largely producing spare parts for existing motorcycles.
In December 1994, BSA Group was taken over by a newly formed BSA Regal Group. The new company, based in Southampton, has a large spares business and has produced a number of limited-edition, retro-styled motorcycles.