(Soviet cosmonaut Alexei Leonov performed the first EVA using a self-contained oxygen backpack, and thus did not require an umbilical.)

Later designs (first used on the Apollo program lunar EVA in 1969) did not need spacecraft umbilicals, instead employing backpacks for self-contained oxygen, electric batteries, and radio communication.

It is part of the life support system and will usually be inspected before use, and maintained and tested at specified intervals.

[1] The umbilical components are connected to the appropriate connectors on the diver's equipment, mostly on the helmet or full-face mask, and the strength member is usually attached to a strong D-ring on the diver's harness using a screw-gate carabiner or similar connector which will not accidentally release or snag on lines.

[2][3] For shallow water surface supply air diving, the diver's umbilical is typically a 3-part umbilical comprising a 3⁄8 inch (9.5 mm) bore breathing gas hose, 1⁄4 inch (6.4 mm) bore pneumofathometer ("pneumo") hose, and diver communications cable, which usually also serves as a lifeline strength member.

The umbilical serves as a lifeline and must be capable of lifting the diver out of the water safely.

[1] Maximum permitted service life for rubber breathing air hoses is 12 years, but synthetic (unfilled polyurethane elastomer) lined hoses may be used without time limit while in good condition as long as they pass inspection and testing.

A common length established by custom and experience is 30 metres (98 ft) for a closed bell diver's umbilical, but this may be varied when circumstances require.

Deployable length may be controlled by tying off the umbilical at the rack to reduce the risk of the diver approaching known hazards too closely.

The purpose of the TMS is to lengthen and shorten the tether so the effect of cable drag where there are underwater currents is minimized.