Method Credit: Lex, Deadcode
This map can be done in one turn, and I believe this is the only reliable way to do it. And the mission record shows another awesome route that's hard to pull off. It hinges on one extremely precise HHG placement, which took me many hours to figure out, and then even more to make sure it was reliable. Since a tiny difference in HHG location makes a big difference in where you're blasted, this placement ended up getting into sub-pixel territory.
Turn 1: Rope and snag the double damage crate, while setting off the right mine to move the right worm to a better spot. Avoid that closer mine. Now get yourself into position at the bottom of this light brown object, facing left:
Now go 4 nudges right (the 1st nudge is your worm getting higher), aim to the 11th angle, toss HHG with the bare minimum power, then move 2 nudges left. Might want to memorize this crosshair position on the blue wire:
The hardest part is tossing a lowest power shot, it can help to take a second to visualize it. With practice you can definitely get it most of the time. Your worm flies up and grave damages the top worm into the water, scoring a triple kill.
Backup Strategy: Rope and kill with dyna if you miss the upper worm.