Again, I would rather have a GPMG over a HMG for infantry use in the jungle. It will be much more versatile on the offensive, which is what we're planning to be on. Unless people are convinced that we can make a HMG that's the weight (and thus man-portability) of a Sorraia, which is really quite impossible. And no, saying that it's on a cart is silly, unless you plan on asking our infantry to drag wheeled carts through the jungle.
Oh, and for air-to-ground, the War Horse would essentially be replacing the AS-AC18s on our aircraft, NOT the Sorraias. It is flat out impossible to replace the 7.62mm MGs with .60 cal and expect similar performance, so I can only assume it's meant to replace the AS-AC18s instead to make sense. And I'm not comfortable with replacing an autocannon design we've already used to great effect with an entirely new weapon, with a lower RPM. Let's just revise the AS-AC18 to be better instead.
It's definitely going to be a lot more portable than a 20mm cannon, that's for sure. We're talking about a 15mm here; if the American infantry can lug this around by hand in weapons platoons then we'll be fine. Honestly though I wouldn't mind a downgrade to 13mm so it was in a more proven size.
A lot of our aircraft are capable of carrying bombs in addition to their cannons and machine guns. The impact of replacing 7.62 with 15mm for fighter missions will be negligible.
I was not talking about making the AS-AC18 infantry-portable either, merely pointing out how the War Horse will not be anywhere near as usable by infantry as everyone seems to think. Quoth the Wikipedia:
Besides vehicle-mounted weapons, the heavy weapons companies in a World War II U.S. Army infantry battalion or regiment were each issued one M2 Browning with tripod (ground) mount. Mounted on a heavily sandbagged tripod, the M2HB proved very useful in either a defensive role or to interdict or block road intersections from use by German infantry and motorized forces. Hearing the sound of an M2 could often cause enemy infantry to take cover. There are numerous instances of the M2 Browning being used against enemy personnel, particularly infantry assaults or for interdiction or elimination of enemy artillery observers or snipers at distances too great for ordinary infantry weapons.
The M2HB was not widely used in the Pacific campaign for several reasons, including the weight of the gun, the nature of infantry jungle combat, and because road intersections were usually easily outflanked. However, it was used by fast-moving motorized forces in the Philippines to destroy Japanese blocking units on the advance to Manila. The quad mount .50 was also used to destroy Japanese emplacements.
HMGs are more of a defensive weapon, and I believe we are now committed to offence in the jungle. The last bit of that paragraph also states that the M2 Browning in the Pacific War was pretty much only useful on vehicle-mounting, not in the infantry role. It will not be a good addition to our infantry arsenal. (incidentally, the Pacific campaign was conducted in jungles very much like the one we are fighting in)
Also, your last argument is slightly fallacious. MG+bombs will be definitely less than HMG+bombs, unless you're proposing sacrificing bomb capability for exchanging the Sorraias to War Horses. (which, for the record, I am absolutely okay with after
that incident, just pointing out that that's going to happen)