In 1963 Natick Laboratories developed a tropical rucksack for the Army of the Republic of Vietnam (ARVN).
The lightweight rucksack with aluminum frame was developed by Natick Laboratories for cold weather and mountain use as an initial effort to develop lightweight load-carrylng equipment in 1961. It weighed 3 pounds (1.4 kg) as compared to the 7.5 pound (3.4 kg) cotton rucksack with steel frame which it replaced.
The tropical rucksack is a nylon version of a cotton rucksack for ARVN forces. It has a longer back and more capacity.
The MOLLE 4000 rucksack fills the gap between the large and medium rucksacks for paratroopers.
The MOLLE II Large Rucksack has an approximate internal volume of 2900 cubic inches in the top compartment and 830 cubic inches in the lower compartment, and is capable of carrying a 120-pound load.
The MOLLE II medium rucksack has a volume of approximately 3,000 cubic inches.
Military specification MIL-F-43356 covers an aluminum frame and cargo support shelf used with the lightweight rucksack.
Military specification MIL-R-43574 covers the tropical rucksack.