Help with the Is-Was

[Lionfish298]

Hey guys, using the oh-so-helpful community made printable is-was-es, I have constructed two pretty beautiful versions. One is the attack course finder angle thingamajigger, and the other is the whiz wheel that I have no idea how to use.

I was wondering if anyone could help me with learning a function on the attack course finder and then with just using the whiz wheel in general. On the HNSA webpage, one finds:

The fifth transverse mark on the periscope pointer is a line engraved across the disc at right angles to the line of eight. This line is graduated in units of measure the same as those on the sight line with sub-divisions of half units; these divisions project above the transverse line only. See O.D. 549 for instructions for modifying instruments not having this line.

4. To use the instrument: (Plates I & III)

(a) Set the Compass rose (2nd disc) so that own course will appear opposite the 180 degree mark on the azimuth card.

(b) Make an observation and determine the bearing of the enemy by periscope and the angle on the enemy bow, i.e., the angle made by the enemy course and the line of sight. Set the periscope pointer to the periscope bearing on the "azimuth card" and read the enemy compass bearing from the compass rose as indicated by the opposite pointer. Set the enemy card to the "angle on the bow" (port or starboard) as measured from the line of sight, and read from the enemy's head on the compass rose the enemy heading by own compass. The 90° arm toward the enemy will indicate on the compass rose the desired heading by own compass to close the enemy on a 90 degree bearing.

(c) To determine the "firing course", turn the Pointers until the periscope pointer is coincident with the desired track angle, as measured on the enemy card; then the other end of the pointer will indicate on the compass rose the desired heading by own compass for the firing course.

5. EXAMPLE: Heading by compass 230 degrees. Enemy relative bearing by periscope 315 degrees. Angle on the enemy's port bow 25 degrees. Estimated range 5000 yards. Desired track angle 110°.

SOLUTION: (a) Set the compass rose for own heading, 230 degrees, to 180 degrees on azimuth card.

(b) Set the periscope pointer to the enemy relative bearing, 315 degrees, on azimuth card, and read from the opposite pointer on compass rose the enemy compass bearing, 185 degrees.

(c) Set the enemy card for the angle on the enemy's port bow, 25 degrees, with reference to the line of sight. Read off enemy course from the enemy heading on the compass rose, which is 30 degrees. The range being 5000 yards, the divisions on the line of sight and the squares etched on the enemy card show that the enemy will pass about 2100 yards abeam if a steady course is maintained and the submarine steers a parallel course, or "lies in wait"; also that the enemy must gain a distance of about 4500 yards to draw abeam the initial position of the submarine. The right angular pointer toward the enemy will indicate on the compass rose a course of 95 degrees if the submarine is to steer a course at right angles to the enemy bearing to close the enemy.

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(d) Turn the periscope pointer to 110 degrees on the enemy card (port side) and read. off 100 degrees from the compass rose on opposite end of this pointer for the firing course for a 110 degree track angle.

(e) With the Course Finder set as stated in 3(c) above to find the distance to close the enemy, each division on the periscope line and whole division on the fifth transverse line referred to in 3(e) above, will then equal 1000 yards. The interception of the enemy's course with this transverse line will graphically show that the submarine will have to travel about 2400 yards on the collision course before actually crossing the enemy track. Therefore the Submarine may employ its top speed, submerged, keeping in mind the Submarine's advance and transfer, and swing on to the collision course running at top speed totally submerged until about 1400 yards have been covered towards the enemy, this then leaves about 1000 yards to close at slowest speed, thus eliminating the possibility of getting in too close. This permits the submarine to be in a position to push home an attack. In making a submerged run on the collision course, the range keeper may be employed. This is accomplished by setting the courses and speeds of the enemy and own vessels on the range keeper. By setting the range as found by the course finder to 2400 yds. the range keeper will show when the 1000 yard range is reached. The submarine can then come to the surface so as to observe the enemy thru the periscope and then maneuver to make the attack. For description and. operation of the range Keeper Mark II see O.P. 460.

1. What is it that we're actually trying to solve for?
2. How do I solve for it?
3. How do I operationalize it/put it into practice?

Also, this "SPEED OMNIMETER"... does anyone...

1. Know how to use it and...
2. Is willing to explain it to me, please?

Sorry to be asking so many questions lately, I seem to just be a leach on the community. I'll be more than happy to start giving back when I'm able.

Everyone's been great.

[tomoose]

Questions and answers are what this forum is all about, LOL. No worries.
I have my own cardboard/acetate version of the is-was and I use it to confirm the targets course and in conjunction the AOB.
I don't believe my method is "by the book" and some other expert will no doubt correct me but....(kinda hard without pictures but here goes).
1. Set your sub's course on the appropriate disk
2. Dial the periscope heading (to the target) using it's 'disk'
So now the is-was should be representing your course and the angle your periscope is at when looking at the target.
3. Turn the target ship disk so that it resembles as close as you can determine the AOB you are seeing in the periscope. Read the targets course from the disk. Now I can use that info and do a rough plot on my nav map (I never use the attack map). The key piece to add is range then tweak the plot appropriately.
Personally, using the is-was disk and comparing that with my TDC and manual-targetting results generally confirms if I'm doing things right. If I get a completely different target course on the TDC than with the is-was then I know I've screwed something up.


As to the Omnimeter, have a look at this thread. I've created a test virtual slide-rule omnimeter but have only toyed with it so far as the graphics are limited at the moment (see thread for details). It seems to jibe with the periscope graduations but more testing is required once better scaled graphics are available at which point I'll release it.
I'm not sure if that's the same omnimeter you're referring to but.....
http://www.subsim.com/radioroom/showthread.php?t=169857

Hope this helps a wee bit.