With the increased interest in tanks in the late 1920's and early 1930's it quickly became apparent that the infantry would need a platoon weapon to counter the armor threat. What most armies looked for were similar weapons to the Mauser Anti-tank (AT) Rifle developed by the Germans at the end of World War I.
The idea behind an AT rifle is to punch a solid hole through an armored vehicles hull by using a high velocity round. Once the round punches through, it will rattle around the inside and do major damage to the crew and any equipment it manages to make contact with. While it may sound odd that a .55 caliber (14 mm) round could stop a tank, the Mauser AT rifle of WWI fired a 7.92mm round. What made the round effective was it's velocity and its penetrating power. Typically AT rounds were tungsten core rounds which allow them to penetrate steel where other rounds would have bounced off.
Design of the Boys (sometimes incorrectly spelled Boyes) AT Rifles began in 1934 and it was officially adopted in 1937. At the time of introduction, the Boys could actually defeat the armor of virtually every tank in existence. Initially the gun was known as the Stantion Gun but was given the name Boys when it's inventor died. The rifle was never popular among the troops not because it was ineffective but because it was extremely loud and had a horrendous recoil. Indeed its recoil was such that it earned the not so affection nick-name "Charlie the Bastard". If one did not hold on tight, the rifle would definitely result in a bruised or dislocated shoulder.
By 1940, many of the armies of the world had developed tanks that made AT rifles obsolete. Fortunately for the British, two of their main adversaries still operated some tanks that were as obsolete as the Boys AT rifle. The armor of several Italian tank could be penetrated by the Boys AT rifle, as could most Japanese tanks. It was also capable of penetrating the armor of some German armored cars as well as Panzer I tanks. So while the AT rifle had really out lived it usefulness in most places, it was still a somewhat effective weapon in the Western Desert.
And it could also be used against fortified positions. Its armor piercing round doing effective work against concrete emplacements fuel trucks and parked aircraft!
The major drawback of the Boys, other than its recoil and report was that it was a bolt action rifle giving it a slow rate of fire. Mounting the rifle on a vehicle solved the recoil problem and increased its accuracy. The rifle was often mounted on armoured cars in universal carriers in place of a machine gun.
The LRDG considered the weapon somewhat useless for three main reasons. It was heavy, it had a slow rate of fire and patrols normally were able to avoid enemy armor. Once they were able to acquire .50 MGs, the Boys rifle was normally not carried. This would lead to some problems during the Barce raid, as the Vickers Mk. V 1/2 inch was not capable of penetrating the 14mm frontal armor of L3 tanks whereas the Boys AT rifle could have. As it was the raiding party had to ram L3 tanks with their trucks, on at least two occasions, in order to withdraw from the city after the raid. This disabled the trucks and eventually left the patrol with only two vehicles for the long ride home.
-- See Also "Stop That Tank" A 1942 movie produced for Canada by Disney