The BBC television series and other depictions have done a disservice to the real Home Guard, which was composed of deadly serious volunteers who believed invasion was imminent.
Many of the guard were in fact fit young men in reserve occupations which meant they could not join the regular forces, Dr Peter Johnston, collections content manager at the museum said.
He said: “I think the popular culture depiction has done them a little bit of a disservice. In a lot of cases, it was more a lads’ army, than a Dad’s Army.”
Documents and artefacts outlining the reality of the Home Guard will go on display when the museum reopens in November after a two year refurbishment.
Records show half of some units were aged in their mid-20s or younger. Of the older men, a significant proportion had combat experience from the First World War.
Dr Johnston said: “These were very serious people and these were very serious times. It’s easy to look back and laugh now at people making their own weapons, but it was a desperate time in 1940.”
The Home Guard, which was originally called initially the Local Defence Volunteers, was formed on 14 May 1940. By the end of July there were more than a million volunteers.
With regular forces taking priority for equipment, the Home Guard volunteers were at first poorly armed with their own weapons or obsolete firearms. The original idea was that the guard would act as a secondary defensive force behind the Army, guarding roads, canals and airfields.
But they were soon converted to a more aggressive role to deal with a potential German invasion, Dr Johnston said.
The German forces planned to push north and encircle London. The German plan estimated that if they advanced as far as Northampton, the UK would surrender.
If the Home Guard were to stand and fight well-trained and well-equipped German troops who had pioneered and mastered Blitzkrieg warfare, they would suffer enormous casualties for little gain it was decided.
So the guard was reimagined as a guerrilla force that would limit the German advance.
Dr Johnston said: “They would be a secret army, sabotaging and attacking the enemy from the rear, slowing them down to buy time for the regular Army to regroup further inland and re-establish defensive positions.”
The Home Guard drilled twice a week, took part in regular camps, and was trained by the regular Army. Within a short space of time it was probably the equivalent of today’s Army Reserve, he said.
Life in the Home Guard was also dangerous with 1,206 members being killed in the war.
Though the invasion never came, the Home Guard remained active in British defence and manned anti-aircraft guns. The Home Guard was stood down in December 1944.
Dr Johnston said: “Had the invasion come in the summer of 1940, the Home Guard would undoubtedly have fought with great commitment but probably been able to accomplish little. But the longer the delay in the planned German invasion went on, the stronger the Home Guard, and British forces overall, became, and better able to resist any prospective assault. They were a vital part of Britain’s defences throughout the war.”