CanadaStamp, Greetings:
" ... why would you register a handwritten note anyway?"
This aerogramme is clearly 'stunt mail', a topical category soon to be recognized by the ATA.
Not that 'stunt mail' is anything new. Surely, we all remember Pat Herst's 07/Dec/1941 'opportunistic mailings' (a nicer term) (also of my own invention, perhaps) to fictitious addresses in Nazi Germany; as the US was now in the war, he figgered (correctly) that the covers would be returned with all sorts of interesting wartime markings. (You've got to admire that kind of focus, eh?)
Back to the 'stunt mail' aerogramme at hand:
The Egyptian Army entered Gaza in 1948, and remained until being expelled in 1967.
Our postmark is 10/Dec/1956.
Israeli troops entered Gaza on 29/Oct/1956.
You can learn more than you want to know at
http://en.wikipedia.org/wiki/Suez_CrisisIsraeli soldiers would need postal service. Given that the bureaucratic mentality is the only constant in the known universe (not a phrase of my own invention), it is hardly surprising that Reshut HaDoar (the Israel Postal Authority) would see fit to postmark all mail originating in Gaza as, well, having originated in Gaza.
The piece may have been registered a) to aid in its not getting lost, or b) to create the up-rating noted by Bujutsu, or c) both.
Clandestine mail is a different topic, and worth a visit to the excellent:
http://www.josefwallach.com/Cheers,
/s/ ikeyPikey