What is the etymology of the word "gong" in reference to medals?

Gong meaning a military medal probably comes from the idea of the ceremonial sounding of a gong:

• (also gonger) An opium pipe (1914+ Narcotics)

• A military decoration; medal or ribbon (British WWII use)

  • both senses probably from gong, ''saucer-shaped metal bell,'' of Malayan origin; the sense ''opium pipe'' may be related to the general association of gongs with Chinese matters, and the military sense to the notion that a decoration is something like the ceremonial sounding of a gong.

(The Dictionary of American Slang, Fourth Edition by Barbara Ann Kipfer, PhD. and Robert L. Chapman, Ph.D.)

The word gong entered the English language via the 17th C. trade routes from Asia, where it denoted a disc-shaped metallic signaling device. Although we may draw a drapery of anglophonic ignorance over the Asian etymology of the word, it's fair to guess that onomatopoeia played a role.

See Dictionary.com for a quick rundown

Fast-forward to the 20th C., when British soldiers, no doubt wishing to affect a debonair and well-traveled mien, referred to their disc-shaped metallic military decorations as gongs in raffishly feigned deprecation.

Oh, hullo Threepwood. Nasty business with those 109's over Bremen; good they gave you a gong for it though.