The Improved Load Bearing Equipment (ILBE) is a load carrying system designed to provide a durable and lightweight means for the deployed Marine to transport individual combat clothing and equipment, and replace MOLLE.

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 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.

The modified commercial Backpack Subsystem (UM21) contains a backpack, patrol pack, and butt pack. The backpacks state-of-the-art internal frame affords a stable platform sufficient to carry 120 lbs. effectively. The backpack transfers load efficiently from the shoulders to the waist and provides adjustments to fit the 5th - 95th percentile male SOF operator. The butt pack attaches to ELCS or the backpack; the patrol pack attaches to the backpack, and is compatible with the other SPEAR BALCS components.

The Corpsman Assault Pack (CAP) is an improved design to replace the previously fielded MOLLE Medical Bag.

The Corpsman Assault System (CAS) is specifically intended to provide the Corpsman with a load carriage system that fully integrates with the USMC Pack and currently fielded body armor systems.

The USMC pack system is specifically intended to provide the Marine with a load carriage system that fully integrates with currently fielded body armor systems.

The Assault Pack of the USMC Pack system has an approximate internal volume of 1525 cubic inches in the main compartment and 300 cubic inches in the front pocket. The Main Pack and Assault Pack components are capable of carrying a maximum combined load of 120 pounds.

The Main Pack of the USMC Pack system has an approximate internal volume of 3400 cubic inches in the main compartment and 1600 cubic inches in the lower compartment. The Main Pack and Assault Pack components are capable of carrying a maximum combined load of 120 pounds.

The large field pack with internal frame is used to transport the individual's existence load in all environmental conditions. Even load distribution is achieved through the adjustment features. The patrol pack is used for short missions, and can be attached atop the field pack.

The combat patrol pack was designed for short missions and offers 1200 cubic inches of cargo space in two compartments.

The MOLLE main pack has a volume of approximately 3,000 cubic inches.

The MOLLE patrol pack has a volume of approximately 1,200 cubic inches including the outside pocket.

The MOLLE II Assault Pack has an approximate internal volume of 1525 cubic inches in the main compartment and 825 cubic inches in the large front pocket that is specifically sized to house a removable six magazine bandoleer or a standard protective mask and allow quick and easy access to it, and is capable of carrying at least a 60-pound load to include the current family of field radios including SINCGARS and ASIP. The radio can be carried in a radio pouch attached to the rear panel of the pack utilizing the 1 inch oval loops.

The MOLLE II patrol pack has a volume of approximately 1,500 cubic inches including the outside pocket that is specifically sized to house a standard protective mask and allow quick and easy access to it, and is capable of carrying at least a 40-pound load to include the current family of field radios including SINCGARS and ASIP.

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-C-41823 covers a camouflage cover for the lightweight rucksack.

Military specification MIL-F-43356 covers an aluminum frame and cargo support shelf used with the lightweight rucksack.

Military specificatin MIL-F-43832 covers one type large size combat field pack fabricated from olive green nylon duck, webbings, tape, coated cloth and metallic hardware.

Military specificatin MIL-F-43833 covers medium size combat field pack fabricated from nylon duck.

Military specification MIL-F-44324 covers the IIFS large field pack and combat patrol pack.

Military specification MIL-R-1619.

Military specification MIL-R-43373 covers a lightweight rucksack made of OG-106 nylon fabric.

Military specification MIL-R-43574 covers the tropical rucksack.