Gray mode

Gray mode was an alert status used aboard Federation starships.

When in gray mode, the starship ran on reserve power, cutting power to non-essential decks and ship systems. It allowed for maximum power conservation, budgeting a starship's energy resources during a time of crisis, while still maintaining an operating status. Gray mode could be invoked during a massive fuel shortage, or when the tactical situation required a reduction in discretionary energy usage.

A number of ship systems were either reduced to a lower operating status, or shut down completely, including:
 * The warp core, which was brought to a cold shutdown
 * Inertial damping and structural integrity systems, which were operated at minimum output
 * Tactical and lateral sensors, which were only used for primary ship functions
 * Deflector systems, which were either shut down, or reduced to minimum levels for non-flight operation
 * Weapons systems, phasers and photon torpedo launchers, were brought off-line
 * Shuttlebay operations were suspended, as the shuttlecraft could provide energy support if necessary
 * Life support systems were brought to minimum levels, and shut down on non-essential decks
 * Transporter usage was terminated
 * Turbolift usage would be suspended at the commanding officer's discretion
 * Food replicator were not used, and emergency rations were distributed
 * Holodeck or holosuite usage was terminated

The recycling of non-essential items, which could be broken down into raw matter patterns by the replicator, was commonly practiced. Preserving the replicator for usage only during critical situations (such as replicating repair tools, medicine, etc.) could help extend the energy resources of the ship.

Starships were often forced into this condition, due to tactical situations or spatial phenomena, which can also coincide with a red alert. During the year-long temporal conflict with the Krenim Imperium, the USS Voyager entered a reduced power mode. 

Gray mode was used aboard the USS Voyager in 2374 when its supply of deuterium was almost depleted, allowing the ship to conserve its reserves for as long as possible. 

The following year, Voyager entered gray mode in an attempt to sneak past a Devore sensor array near the Tehara system. 

Modus Grau