Development of the Tropical Rucksack (a.k.a. Jungle Rucksack) began in 1965 when MACV requested a nylon version of the ARVN pack from Natick Labs for evaluation purposes. However, after initial testing the rucksack had to be significantly redesigned in order to strengthen the pack and round off the corners of the frame.1 The redesigned rucksack was assessed against three Cresson H. Kearny modified Gurkha-Australian packs, before being finally approved for procurement in early 1968.2
The standardized Tropical Rucksack featured an OG-106 nylon pack with three outside pockets mounted on a spring steel X-frame. The outside pockets and the main compartment were provided with removable waterproof treated nylon liners, though these were often poorly coated and prone to leak.3 The map pocket inside the top flap did not have a liner but the underside was waterproofed. The outside pockets had strap and buckle adjustable closures and snap fasteners for quick access, whilst Velcro sealed the map pocket.
Webbing equipment hangers were located around the top of the bag and tie straps were positioned on each side of the pack. In addition, two loops were provided on the bottom of the rucksack and two on each side for attaching extra items.
The Jungle Rucksack was slightly heavier and more expensive to produce than the Lightweight Rucksack, but offered quick-release buckles on both shoulder straps, greater carrying capacity and fewer projections to get snagged on the undergrowth.In addition to replacing the Lightweight Rucksack, in January 1968 ACTIV recommended that combat / combat support units in Vietnam be issued the Tropical Rucksack rather than the M1967 butt pack.41. Support To United States Army In Vietnam - Clothing & Equipment (United States Army Material Command Feb 1967)
2. Support To United States Army In Vietnam - Clothing & Organic Materials Vol II (United States Army Material Command Aug 1968)
3. Jungle Snafus...and Remedies by Cresson H. Kearny (Oregon Institute Of Science And Medicine 1996) (Amazon.com affiliate link)
4. ACTIV Final Report - Lightweight Loadbearing Equipment (Army Concept Team In Vietnam January 1968)