The Sierra Defense Fleet was founded when Starfleet completed the
construction of the asteroid detection outposts along the Romulan
Neutral zone in 2266. The SDF was intended as the first response fleet
should the Romulans ever cross the neutral zone and war be declared.
Over the years the SDF has taken part in many noteworthy actions in the
region, including forming the armada led by Jean Luc Picard to stop
Romulan intervention during the Klingon civil war in 2368 and forming
Battle Group Omega which was deployed to support the Enterprise E in
2379 when Praetor Shinzon’s plot was uncovered.
In the late 24th
century the dynamic of the Sierra sector began to change a great deal
as the Romulan Empire recovered from the actions of Reman Praetor
Shinzon. As a result, the Sierra Defense Fleet was engaged less as a
battle formation and more as a diplomatic and humanitarian armada.
During this time the fleet maintained its title and tradition purely
through the efforts of its members who lobbied command to keep the
formation intact. Even though Starfleet temporarily granted this
request, in 2385 the Sierra Defense Fleet was officially listed as
decommissioned. Several Admirals working quietly behind the scenes and
outside of traditional Starfleet regulations endeavored to keep the
fleet intact and operating under it's traditional moniker. Though not a
rogue operation, the SDF was no longer directly under the control of
Starfleet, and was granted certain latitudes in order to guarantee the
security of the galaxy at large. Instead of being assigned ships by
Starfleet command, the SDF now recruited their members from the best
and brightest officers available, accepting only those who both
understood the nature of the assignment and could handle operating
outside of Starfleets direct influence.
When the Hobus star went
supernova in 2387 the region was once again thrown into turmoil. With
the Romulan government in disarray their military commanders began
acting on their own authority and the security of the region was once
again jeopardized. As a result, Starfleet command sought a means to
bring stability to the sector once more. It was at this time they
became aware the SDF was still in operation, without sanction.
Unable to either deploy an entirely new fleet to the area or exert
control over the SDF in any official manner, Starfleet contacted the
Fleet Command to broker an agreement. The SDF would once again enjoy
the support of Starfleet, provided they were willing to accept mission
assignments from Starfleet Command. This agreement was accepted on the
terms that the SDF would not be subject to direct oversight from
Starfleet Command, nor the council.
The Sierra Defense Fleet
continues to operate with this mandate while working with Starfleet
command and other military and civilian organizations in an attempt to
bring stability to the area once again. Although primarily a military
formation, the Sierra Defense Fleet has adopted the traditional
Starfleet goal of exploration and scientific discovery while not
engaged in security activities throughout the galaxy.