11 across: Heat of battle sees legend annihilate army base (6)
Super surface reading: battle sees legend annihilate army base = war sees myth annihilate y = war myth – y = warmth = heat.
12 across: Male companions pejoratively help kid’s reservation (8)
I love a good piece of slang, and this comes with two: help kid’s reservation = hand bags = handbags = male companions.
16 down: I help stars quash essentially taboo triangle (9)
Anything with maths gets my vote: I help stars quash essentially taboo = I sos celebs quash b = isosceles = triangle.
26 across: A watchful rear in men-only prison (6)
Hilarious surface reading: a watchful rear in men-only = a l in stag = stalag = prison.