Just dug up the above and it occurs to me that this seems to be an anti-magnetic version. Compass needle doesn't even twitch whereas another that I have, a black dial Unitas movement version, has a plated brass case and is distinctly magnetised. Investigating a little I find that anti-magnetic variants (of other models) have been issued to radio operators. Is this perhaps one of those? I can't find any other similarly cased versions. Like most of the rest of my 30 year hoard it has to go so I'm wondering if it may have some additional rarity value? I'd appreciate any feedback.