Has ECM and a big punch. Ghost heat from 2x MRM 40 is laughable. Blast away with the AC20 for 100 damage with decent mid-range coverage. Small lasers for lights or anything else that gets too close.
Drops the lasers, makes a dead arm, and drops armor on dead arm to fit max engine. If you want a few small lasers, you could swap a heatsink if you aren't too worried about heat and/or strip more armor. Endo-steel version to increase available tonnage. Has slightly better armor and an extra heatsink. However, requires endo, which limits slots for ammo. Swapping one MRM40 for 2xMRM20 freed up another slot for ammo, but MRM20s add an extra 2 tons, which somewhat counteracts endo benefits. Not much to do with the tonnage anyways except add armor to dead arm. Alpha ghost heat is probably worse, but you have better cooling efficiency with the extra heatsink and without the lasers, and could chain fire. Haven't tried it, due to endo.
Extra 5.23 heat for using MRM40 + two MRM20s. I found the arm mounted weapons to be very important for deterring light mechs.
