Hi guys, first post.

My own WWII-era CKC MKIII prismatic compass developed an approximately 11mm wide air bubble after recent air travel. I came upon a very quick and easy way to get a bubble out of Silva compass capsules and thought I'd give it a go on my MkIII prismatic.

Here's what I did, step by step...

Step 1. Put the compass on a window sill in direct sunlight on a sunny day.

Step 2. Check the compass after a couple of hours and you'll see the bubble has either gone or reduced in size.

Worked for me.

Plan B was going to be to strip the compass and do a complete refill using purified kerosene (plain lamp oil). I haven't ever done this, but the idea is that you take the capsule out of the case and crack the filling screw carefully so as not to damage the o-ring. Remove the screw and submerge the compass capsule in purified kerosene, manipulating the capsule to (hopefully) manoeuvre the bubble out of the filling port. Replace the filler screw while the capsule is still submerged, wipe it clean and wipe some clear varnish over the edges of the filler screw. Then reassemble the compass. Once again, I'd like to point out that I've never performed that particular bubble removal technique so if anyone's compass explodes...

Try the window sill/sunny day method first.

That's a pretty case. A very Great War-looking piece of kit. It looks a little too big for the MKIII, but it's my understanding that they were also made for military engineering instruments such as barometers. I had one I picked up off ebay a while ago and discovered that it was too big for my compass by about 5-10 mm on all sides and that under the "leather" it was made from cardboard. I've also got an Enbeeco M88-ish prismatic compass which came with a similarly-constructed case, but with the correct dimensions, and it too was coated cardboard. I ended up buying some leather hide and I'm going to have to make my own for my MKIII and my US Verner's Pattern prismatic. For outdoors use, the MKIII rides in a Canadianicon issue webbing pouch.