Zealous and eager.
This is an adaptation of the Chinese kung - work, and ho - together. The Anglicized term gung ho became widely known in English as a slogan that was adopted in WWII by the United States Marines under General Evans Carlson. The New York Times Magazine reported this in 1942:
"Borrowing an idea from China, Carlson frequently has what he calls 'kung-hou' meetings... Problems are threshed out and orders explained."
The following year Life magazine reported:
"He [Carlson] told them [the Marines] of the motto of the Chinese Co-operatives, Gung Ho. It means Work Together... My motto caught on and they began to call themselves the Gung Ho Battalion."
The first record of gung ho in print was a little earlier. In October 1941, the Oakland Tribune reported a story about some captured short war films. This doesn't mention Carlson or the US Marines by name, but the films relate to their activities:
"Other shorts are 'Information Please' and 'Gung Ho' with Regan McCrary."
See other phrases that were coined in the USA.