Your grandfather was a part of a very important activity.
Churchill had just formed the new government, at the same time as Germany's invasion of France, 10 May 1940. That invasion posed an immanent danger to Britain, which feared the same fate.
In the same time frame, the Germans had backed the British Expeditionary Force back against the English Channel, so the threat was very real.
On 14 May 1940, the British War Secretary, Anthony Eden, sent out an appeal by radio for able bodied males 15/65 to volunteer for defense against a possible German invasion of the island.
It is reported that within 24 hours there were an estimated 250,000 volunteers, who were organized under the title Local Defense Volunteers (LDV). By 17 May 1940, the first units were on patrol along the Kent coast.
They were civilians under command of the army.
In July 1940, the name was changed to Home Defense Guard (HDG).
Uniforms were all but non-existant early on, and the units drilled with make-like rifles until real weapons were secured. An early weapon was a large number of 30 caliber 1918 Springfield rifles, which were supplied by the United States.
Otherwise, the men armed themselves with weapons from their homes, shotguns, pikes, pitchforks, whatever they could come up with.
The HDG grew as the war progressed, becoming a well organized activity, covering all of Great Britain with its own training schools and local administration. Some units took over anti-aircraft duties.
In addition, there was a marine section, comprised of boat owners who patrolled rivers and lakes.
Several select units were trained in acts of sabotage and guerilla warfare. They were to go "undergraund" in the event of a German invasion.
There were an estimated 1,,750,000 men in some 1,1000 county and district battalions at the peak of the HDG.
The units were told to "stand down" at the end of Nov, 1944, when the threat of invasion had passed.
That is about all that I can report to you on the HDG.
With best regards,
Louie F. Turner.
What is the season in your part of the world ? It is cold (49F) and wet here in Texas.