If you need an introduction to the concept of machine guns, our good friend Rambo would like to undertake that courtesy on our behalf. We'll just tell you that older machine guns often ran so hot they had to be handled with oven gloves while the barrels were changed. So obviously, when they weren't dealing hot metallic death to whatever ethnic group it was cool to kill that day, they did double duty ... as teakettles.
Not pictured: Chamomile.
Those older machine guns often had large bags attached to the side, filled with glycerin, water or, if all else failed, even the soldier's own urine. Regardless of the liquid, whatever was in the bag became boiling hot after the gun was fired. Never ones to waste resources, those wily Brits often used the preheated bags to make cups of tea with the excess water. Hopefully, they didn't get the pee-bags mixed up. On a few occasions, soldiers were even observed firing off bursts for no reason other than to simply heat the water, because the guns could bring water to boil in less than a minute -- way faster than any other heating method they had access to. That's right: The very first commercial microwave ... was a Vickers machine gun.
There's nothing like a hot cup of herbal tea to go with your mass murder.