The Sikorsky R-4 was a development of the pre-war VS-300. the prototype first flew on Jan 14, 1942.
The first pre-production test YR-4A's had larger main rotors and engines, followed by 27 YR-4B's with a larger cabin.
In '43 100R-4B's were ordered, and 45 went to the RAF.
The R4-B did see use in combat areas, being used for recon and medical evacuation in the Burma theatre.
As to being armed? The pilots were...
I would say a M-2 carbine is almost a weapon

(Yep, small numbers of full auto carbines were used in the last months of the war, with 30 round mags)