[3] With the end of the Battle of France and the evacuation of the British Expeditionary Force from the port of Dunkirk between 26 May and 4 June 1940, a German invasion of Great Britain seemed likely.

[8] When submitted to the Ordnance Board - which remained unconvinced of its merits - Prime Minister, Winston Churchill, witnessed a demonstration of the weapon in 1941 and ordered that it be put into production.

This unorthodox deployment gave the Smith Gun 360 degrees of rotation which, combined with a maximum 40-degree elevation, produced a basic firing-plate-mounted field weapon light enough to be towed behind a civilian vehicle,[9] despite not being designed for this.

(Home Guard units quickly discovered this fact, having to be prohibited from doing so as it would damage the weapon's wheels (and possibly the axle), inhibiting or even preventing traverse.

[10] The low muzzle velocity meant that shells were lobbed in a high curved trajectory, making precise range calculations and firing experience vital.

This was difficult when so few rounds were available for training, a problem compounded by early batches possessing faulty fuzes that led to the Smith Gun's alleged 'terrifying reputation for killing its crew'.

"[3] After a period of initial distrust, many Home Guard units appear to have taken to the Smith Gun and attempted to make the best use of it: Mackenzie states that some units even had 'a growing sense of affection for the weapon' and describes how, when a letter was published in The Times towards the end of the conflict criticizing the weapon, numerous Home Guard volunteers replied with their own letters describing how satisfactory the Smith Gun had been; they also stated that it was 'one of the best pieces of equipment ever issued to the force'.