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 large field pack is designed to carry up to 70 pounds of existence loads which include clothing, personal items and rations.

The medium field pack is designed to carry up to 50 pounds of existence loads which include clothing, personal items and rations.