Just fun to see.

he looks happy as can be

Thanks. I thought that projectile looked a little big for a 105mm.

Your story about swapping M198 to M777 reminded me that in 1966 we trained at Fort Riley with the M-14 7.62mm rifle. Just before we boarded a troop train for Oakland Naval Terminal and a ship to Vietnam, we traded in our M-14s for the original M-16 5.56mm rifle. Didn't even get to fire them until we arrived in country.

Oh, and our howitzers were the M101A1 from the WWII/Korea era. They did the job, though.

Propellant for firing your round. Think gun powder. The more you use the further it goes. I like to think of arty as a triangle. Observers call for fire at a certain point. They call our Fire Direction Center (think nerds playing D&D until time to do nerd stuff to calculate what is need to get a round where it's being called for. Then you have what I did, the brawn of artillery, the gun bunnies (13Bs). The mission comes to us as: number or rounds, type of round, the fuse (point detonating, delay, time etc...) the charge (amount of propellant), deflection (left and right) and quadrant (up and down). We do our thing, pull a string, gun goes boom and observers observe where the round impacts. Adjustments are made if needed and then we fire for effect on said target.

JABQ04, excellent explanation.

If I could, I'd like to add what went on in the Fire Direction Center (FDC) to calculate the data that was sent to the guns, at least how it was done before computers. When a fire mission was called into the FDC by one of the forward observers, the target location was plotted on a firing chart, and the range (in meters) from the battery to the target and the deflection (the angle from dead center of the guns in mils) was determined using a Range Deflection Protractor. Using that information the elevation that the gun tube was adjusted from the horizontal was calculated using a special slide rule for the particular caliber weapon being fired. As JABQ04 has said, the propellant charge was based upon the range to the target.

In late 1967 we received the first field artillery digital computer (FADAC) in Vietnam. It was big, bulky and very simplistic compared to today's computers, but it worked pretty well.

Just one more thing, each step in calculating the firing data was done by two different individuals in the FDC that provided a double check on the data being fired. We even used that double check system to make sure that FADAC was providing the correct data. Interestingly enough, we could compute the initial (first round) data manually faster than FADAC could, but FADAC was much faster and computing subsequent corrections.