By the time that the Battle was entering service in 1937 it had already been rendered obsolete by the rapid advances in aircraft technology. The performance and capabilities of fighter aircraft had increased to outstrip the modest performance gains that the light bomber had achieved over its biplane antecedents. For defence, the Battle had been armed only with a single Browning machine gun and a trainable Vickers K in the rear position; in service, these proved to be woefully inadequate. The Battle lacked other common defensive features of the era, such as an armoured cockpit and self-sealing fuel tanks. The Battle was considered well-armoured by the standards of 1940, although there was an emphasis on protection against small-arms fire from the ground. No RAF bombers were fitted with self-sealing tanks at the beginning of the war, although they were hastily fitted once the necessity became apparent. Since it was some time before self-sealing tanks could be mass-produced, it was a common stop-gap in 1940, even into 1941, to simply armour the rear of the fuel tanks with single or double layers of 4 mm armour. The Battle, along with the rest of the early-war inventory, was taken out of front-line duties before it had a chance to be fitted with self-sealing tanks.