took me forever to S-rank the BAWS arsenal #2 mission. i over-indexed on using melee to save ammo cost and ended up too risky. my winning build was:

• songbirds and plasma rifle
• pulse cannon on shoulder and pulse gun on arm

for each invisible guy, i got close and did one songbird + one plasma. that's enough to kill one. for the final guy in the coral well, i shot both shoulder and arm pulse guns at the same time, managing overheat, to drop the shield. then one songbird + 1 plasma finished him off.

i still had to do it with basically perfect execution to get s rank. i think if you get less than 150k payout, you drop to A-rank. whoof