Media playback is unsupported on your device Media caption Members of the Home Guard trained at locations right across Northern Ireland in the event that Germany could invade.

After the fall of France in 1940, the United Kingdom braced itself for invasion.

As Churchill said: "The whole fury and might of the enemy must very soon be turned on us."

So it was decided to supplement what was left of the regular forces after Dunkirk with a home defence organisation. The call went out on radio for those who wanted to join the Local Defence Volunteers to register at their local police station.

Those who turned up at their local RUC barracks did so in vain - the new force did not extend to Northern Ireland. The Prime Minister, Lord Craigavon, was not having that and successfully lobbied London.

Image copyright SOMME HERITAGE CENTRE Image caption A picture of the Comber Home Guard taken around 1944

However, there was a problem - the Territorial Army associations used to form the Home Guard in Great Britain did not exist in Northern Ireland. So, the LDV was organised through the Ulster Special Constabulary - the B Specials.

The nationalist newspapers complained immediately that this force could not command support across the community.

Home Guard veteran John Luke, who spoke to the BBC as part of a new BBC Radio Ulster documentary Not Dad's Army - Northern Ireland's Home Guard, said that there were a few Catholics in his battalion.

"We had over 300 in our battalion and as far as I can remember there were two Catholics," he said.

"I'll not say they objected, but they didn't join. They weren't aggressive towards us though."

Image caption The Home Guard featured in the BBC sitcom Dad's Army but the reality in Northern Ireland was very different

However, as historian Dr William Butler from the University of Kent discovered, the official figure for Catholic recruitment in what became known as the Ulster Home Guard amounted to 150 men out of a total of almost 40,000.

"The figure of 150 comes from an official request by the British government in November 1942," he said.

"They basically asked the Northern Ireland government for a figure of Catholic participation, because before that they had been pretty vague.

"The Northern Ireland government had to admit it was a very low figure, the figure works out at about 0.5% of the total force."

A further problem was that, being part of a police force, they ran the risk of being shot as partisans for fighting an invading army. The solution was that in the event of an invasion, they would immediately come under army command.

Media playback is unsupported on your device Media caption Major General V.H.B Majendie, commanding officer for NI, appeals for support for the Ulster Home Guard in this recruitment video from 1942

Why didn't the Army simply take over the UHG anyway? It was discussed. Some thought the Army couldn't match the organisation of the Ulster Special Constabulary.

Though the Secretary of State for War David Margesson spoke of "the absolute necessity of not involving the Army in the religious animosities of Ireland".

The Ulster Home Guard was also better armed in the beginning than Capt Mainwaring's Dad's Army. Indeed, the RUC was able to lend the Army 300 Lewis guns after the loss of equipment at Dunkirk.

The veterans themselves seem to have regarded themselves as volunteer soldiers - paying little attention to the connection with the B Specials.

Image caption An original Ulster Home Guard uniform is on display at the Somme Heritage Centre

Their role in home defence - and later that of taking over anti-aircraft batteries - meant that tens of thousands of regular soldiers could be freed up.

It is also argued that their presence provided reassurance to the civilian population.

They were stood down after D-Day, when it became clear the threat of invasion had receded. The Ulster Home Guard was reformed in the 1950s during the Cold War. But that's another story.

Not Dad's Army - Northern Ireland's Home Guard will be broadcast on BBC Radio Ulster at 12:30 GMT on Sunday 1 March 2015. It will then be available on BBC IPlayer radio.