[lormand]

"Those are 105's and the ammo is a much easier to handle plus when you shoot out the door your are shooting direct fire of a sort."

Thanks for the clarification. I thought all Howitzers were 155mm because I am an ignorant civilian. :)

[CatoRenasci]

Field artillery tubes are usually in one of the following sizes:

105mm -- now mostly airborne and reserve
155mm -- now the standard battalion level tube artillery
17mmm -- probably all gone now, maybe some in the reserves or Guard - were very long range, tiny deflection probable error, large renge probable error, biggest problem was short barrel life.
203mm -- the famous 8" howitzer, probably the most accurate artillery piece fielded by any army, ever.

All of these, except 105mm, are usually self-propelled these days, although there are some towed 155mm (M198).

[Robert A Cook PE]

Nothing ignorant about being a civilian at all ..

You just have a different background, and know more about your field than you do about big guns. 8<)

There are actually a few other subtle changes that this allows the Marines too.

A mortar (traditionally) is a local support weapon under local control. It fires "up" and the shell comes down relatively slowly and vertically. Good against trenches and against people hiding behind walls. But it is smaller, often man-portable, so doesn't do much damage. Man-portable means it can move faster when the enemy shoots back, but not as far. And it's heavy! Its shells are heavy! A mortar can't fire "level" directly at attacking troops - and this was needed in Vietnam many times when the enemy ran directly at the perimeter of a camp.

A howitzer can fire "flat" directly at the enemy, or "up" and at long range. It's bigger, but you need a truck, ammo truck, (or two or three) and have to wait to set the thing up. Once you fire, since it takes a while to dismantle and move it, the enemy can "reverse fire" and kill your cannon crew.

So a self-propelled mortar-howitzer solves several problems. Particularly since it has a self-contained GPS system so survey points aren't needed. Stop, fire, move, stop, fire again, move.

Also, the artillery are usually under a higher-level staff command, and so the local commander has to relay fire request up his chain of command, then they go back down to the artillery crew down that chain of command. This can take a while. If somebody else has a competing request for fire, then the first troops have to wait.

As a mortar, weapon seems to be designed to give the local commander local control over a BIG gun.

And local commanders like that. In WWII against the German forts and bunkhouses in the forests, 8" Long Tom cannon crews would drive up outside of machine gun range of a stubborn outpost, literally sight directly up the cannon barrel at the bunker (if no enemy tanks were around!) and "ask" the Germans to surrender. Local fire control away from the division's commanders made that possible.