Greetings artillery experts, I'm publishing my grandfather's fantastic 500 page war journal. He was in the 9th Infantry Division Mine Platoon under Patton. I have run into a specific problem. According to the journal his Lieutenant was struggling with laying his half track mounted 75mm guns and approach him to help with the problem. Joe was in the mine platoon but had surveying experience and could use an aiming circle. He noted that these guns were French surplus from WWI. My specific question: Why did the these guns have no gauge to set the azimuth for the gun? Was it because of the retrofit to the half track? A bad design? Please read in the text below. Still in the editing, so please bear with me. Having trouble making paragraphs indent here too. Thanks in advance! From the book: [SIZE=13.333333333333332px]Lt. Buchanan came over to my slit trench. I found it comfortable to sit on the ground, my feet in trench, while working on my drawing board. He sat down beside me, " Joe what do you know about a clinometer?' It sounded like an instrument a surveyor [/SIZE][SIZE=13.333333333333332px]should[/SIZE][SIZE=13.333333333333332px] know something about, but I didn't. I replied, "Nothing."[/SIZE] [SIZE=13.333333333333332px]He persisted to show me a brass instrument that looked like a bastardized Abney Hand Level - something I understood. He explained that it was an instrument designed to measure the vertical angle of any level surface. When placed appropriately on the breech block of a 75mm gun it measured the vertical angle of the bore.[/SIZE] [SIZE=13.333333333333332px]He had a book of tables. We pored over them while he explained what he knew about the instrument. The tables converted vertical angles into distance for specific types of 75mm ammunition. It soon became clear with the clinometer we could direct the gun to drop its shell at any given distance within its range. Help from an observer could directed it to a specific target after the first volley. "That's fine," I said, "we know how set the distance, how do we lay the gun in the proper [/SIZE][SIZE=13.333333333333332px]direction[/SIZE][SIZE=13.333333333333332px]?"[/SIZE] [SIZE=13.333333333333332px]He said, "That’s why I am here. Captain thought you might be able to help with that problem."[/SIZE] [SIZE=13.333333333333332px]He outlined a possible conversion of our company into an artillery unit if I could sort this out. It seemed like a logical mission for the Anti-tank Company - this secondary capability was feasible if properly equipped. We had the survey skills and ordnance handling experience. We weren't placing many mines in Sicily anyway.[/SIZE] [SIZE=13.333333333333332px]I explained how the aiming circle worked. Set it up and turned several azimuths to show the Lieutenant. Arms crossed and two fingers on his chin, he’d heard of it, but never seen one in operation. I showed how to compute the azimuth between two points on a map, then set the aiming circle to that figure — showing the line of sight.[/SIZE] [SIZE=13.333333333333332px]On several possible firing solutions, we had no problem laying a gun for trajectory or determining the azimuth. Stumped, we still needed to know, how do we to transfer this azimuth to the gun? [/SIZE][SIZE=13.3333px]**I would like to further explain here why there is no instrument on the gun to set the azimuth? - mdpphoto**[/SIZE] [SIZE=13.333333333333332px]Lt. Buchanan and I wracked our brains trying to solve this problem. One of the first possibilities was to set up the aiming circle in the half track, logical enough. Upsetting this solution, I pointed out the aiming circle had a magnetic needle. Its azimuth would be distorted by all the metal in the gun and the armored sides of the half track. A crazy idea, but it led to possibly setting the aiming circle away from the weapon. Sighting a prominent skyline object, say a mountain, then bore-sighting the gun on it, would roughly achieve the target azimuth. The gun would be subject to a small error due to the distance between the aiming circle and the pivot point of the gun -[/SIZE] lines of sight wouldn’t be perfectly parallel, but close enough to range the guns. Possible, but inefficient, and impossible in the dark.