Wasn't the Captain Midnight decoder shaped like a jet/spacehsip and hollow so you could pour a drop of milk in and write invisible messages with the removable nose?

As for Tom Terrific and memory, this from central Norway and most of my life later

I can be a plane up high
A diesel train go roaring by
A bumble bee or a tree
It's me!
When there is trouble
I'm there on the double
From th'Atlantic to the Pacific
They know Tom Terrific

As for the baking soda subs, my Dad used to use a deodorant that came in plastic squeegy bottles (I remember them as green and the sound of wheee-juh, wheee-juh, two doses under each arm in front of a misty mirror in the mild panic to get ready for work/school)anyhow, I'd get the empty bottles, filled with water in the bath tub I used them to strafe the subs when they surfaced...

I should really get back to work...

bassen