The song describes the experiences of Australian soldiers who served in Vietnam during the Vietnam War (American War). According to John Schumann, the song was written for two friends of his.

The subtitle "A walk in the light green" is explained by John Schumann in the spoken introduction to the song on the live album "Caught in the Act": Australian military maps used in Vietnam indicated heavy jungle with dark green coloring, while areas of light jungle were shown in light green. Heavy jungle provided ample cover, and was unlikely to be mined; light jungle meant "no cover, and heaps of mines". 'A walk in the light green' was thus a dangerous assignment, because the soldiers were exposed and in constant danger of stepping on landmines or other booby traps.

'the passing-out parade': completion of basic training ('passing-out') by army recruits is often marked by a formal parade, called the passing-out parade.

'Puckapunyal': Australian army training facility in Victoria, used for basic training.

'Canungra' and 'Shoalwater': other Australian army bases, with specialist training facilities including jungle warfare schools.

'Townsville': town in Queensland, Australia

'SLR': Self-Loading Rifle, a semi-automatic 7.62mm battle rifle used by the Australian and British armies from the 1960's to the 1980's.

'slouch hat': broad-brimmed soft hat worn by Australian soldiers

'greens': Australian military uniform, or part of it. Possibly a reference to the clothing item known as 'trousers, green lightweight'

'Vung Tau', 'Nui Dat': locations in Vietnam

'V.B.': Victoria Bitter, a popular Australian beer

'Chinooks': Boeing CH-47 Chinook helicopter, an American-made heavy-lift helicopter used by the Australian military

'chopper': slang for 'helicopter'

'M-16': a 5.56mm automatic rifle issued to American soldiers and their South Vietnamese allies in Vietnam.

'someone yelled out "Contact!"': in military parlance, 'contact' means encountering enemy forces; the soldiers who first engage an enemy will shout 'Contact!' to warn their squadmates that a firefight is starting.

'dusted off': military slang -- to evacuate injured soldiers, particularly by helicopter

"the day that mankind kicked the moon": July 20th, 1969, date of the first Moon landing

"tinnies": cans of beer

"rec. leave": 'recreational leave' - a short period during which soldiers are off-duty in a safe area such as a friendly town

'Anzac': derived from the First World War acronym for the Australian and New Zealand Army Corps, 'Anzac' is used generally to refer to the Australian military, its history and traditions.

'Channel Seven': Australian television channel

"I Was Only 19 (A Walk in the Light Green)" as written by John Lewis Schumann, Kaho Cheung, Simon Luke Fellows, Dale Anthony Harrison, Shannon Lee Kennedy, Timothy James Levinson, Kenneth Spencer Sabir and Richard Tamplenizza.