Hi buzznelson, first hand information from the men who flew the planes is an excellent source to support the "pickle barrel" derivation of the word. People have been writing about WWII since WWII, so it's odd that the first known occurrence of "pickle switch" in print hasn't yet been pushed earlier than 1960 (excluding references to "Pickle's Switch" in the railway industry before WWI).
My point was that your implied slur that mollusque believes that 'Google provides the answer to all questions' was unjustified. He was simply reporting what he found in the way of citations via Googlebooks.
This version of the derivation sounds unlikely insofar as I've never heard 'pickle' mean release in any dialect of English of I've come across.
I trust your father could also point out the straw man fallacy to you; mollusque was referring to his search for the earliest recorded citation using one of the best repositories of written material that we have access to, i.e. G Books.
"Pickle Switch" was not the official nomenclature of the control the bombardier used to release individual bombs. It was called that by the flight crew that flew the bombing missions. The B17 bombardier had several options when deciding how to begin dropping bombs. He could use a device that released bombs at timed intervals or he could salvo the entire load. The "Pickle Switch" was use when he wanted to release a single bomb. Then he would hold the switch in his hand while sighting through the Norden Bombsight. When he was satisfied he was on the target he pressed the release button that was incorporated in the center of the switch - "Pickling" away a single bomb. This description was related to me by my father who was an engineer employed 41 years with the Boeing Company. During WWII he was the B17 Project Engineer. Further substantiation was provided today, with a telephone conversation with my former Boeing Flight Test boss who was a WWII B17 pilot and flew 25 bombing missions over Europe.
If he was alive today, I can imagine my father reaction to the notion that Google provides the answer to all questions.
Interesting possibility for the derivation, but I can't find any citations of World War II vintage. The first uses of the term in Google Books (1960-1964) all concern activating cameras using a pickle switch. Some of these were aerial cameras, so the term could then have transferred to other aerial triggering functions.
The Norden Bombsight used by American B17 Bombers during WWII often was claimed to be so accurate that, by using it, you could drop bombs in a "pickle barrel". Hence the switch used by the bombardier to release his bombs was referred to as the "pickle switch". Now, any switch use to fire weapons or start a start a particular event may be named a pickle switch.