Taking the first mark will give you the range, and Aob. The second gives you the speed.You also redo the Range and AOB.Retake all readings on subsequent marks updates the TDC and establishes a base course.This requires using a real pencil and paper as well as the scratch pad at the scope or Uzo. It also tells you if there are any speed changes between readings,how long each leg of the zigzag is Etc...It's not as complicated as it sounds.

Not sure when the technology came about, but i suspect the Germans had it first. Instead of using known mast height some advanced periscopes and TBTs (US equivelant of UZO) had a split image - when you rotated the focus so the two images were lined up, that gave you the range. It's actually pretty old technology, I remember reading about a "come up glass" around the time of the War of 1812. My Dad had a 35mm camera from the 1920s that had a similar rangefinder lens.

There are a number of ways to find the range. US recognition manuals not only stated the mast height but had a grid by which you could estimate the range by the relation of the horizon to the target. Another method would be the range finding reticle in the scope, or the dual image rangefinder in the scope, or sonar or radar. The captain would center the target in the crosshairs and the fire control party would recort the relative bearing. The captain would estimate the range by one of the above methods,. and the estimated angle on the bow. That data would be entered into the TDc and the fire control party would enter the location of the target on the map. This would be done several times. Once you enter the position of the target twice, the line between the two locations is the targets course. In SHIII, the ship icons on the map represent the work of the fire control party, except that in order to mark their location you must enter a map mark. Unfortunatly, in SHIII you cant drop map notes like you could in SHII, a big step backward in my opinion,but the little map marks that we are allowed to make do work. I make as many of these obervations as circumstances allow, keeping the scope up only as long as absolutely necessary, 5-6 seconds at the most at close range.

The range is the least important piece of information needed for a fire control solution. I manually set the range at 1,500M and manuver for a shot at about 1,200 M. So far I have had very good results. I recently had a target that was zig-zagging, and by marking its locations at the start of the turns I was able to predict its Zig-Zags pretty accurately.

If you can find the little book that came with the old dos sub sim called Up Periscope, it has a very good description of the work of the captain and the fire control party and the making and keeping of the manual plot. There is also a complete WWII TDC fire control manual online, and a link to it on one of the threads here. I hope you find this usefull. If you have any questions, fire away. Joe S

why in the world did they put this tool in the periscope that we have to use when they could just as easy of used what captains really used as you all know its hell trying to keep the bottom line on the waterline of the ship and try to measure the mast while in a storm and the scopes bouncing all over the place with three destroyers breathing down your neck :damn: I feal like i could adjust these lenses till they matchup versus that thing we have to use :damn: :damn: :damn: could this be modded in somehow