The F.L.A.G. Mobile Unit is a semi-trailer truck owned by the Foundation for Law and Government, which functions as a mobile garage for K.I.T.T. and a mobile Headquarters for Devon Miles to relay information to Michael when Michael's and K.I.T.T.'s missions bring them far enough away from F.L.A.G.'s standard HQ. The Mobile Unit is referred to as just "The Semi" on many occasions, but has also been called "The Rook," "Mobile Office" & "Mobile Base." The Mobile Unit was usually parked or driving around somewhere near Michael's & K.I.T.T.'s location.
During Season 1 through 3, the audience never learns who the driver is. The audience can see the driver on occasion when there is an outside shot of the Mobile Unit. Occasionally the driver is accompanied by someone else, as seen in Knight of the Drones.
In the Season 4, Reginald Cornelius III, or RC3, is officially designated the driver and is seen doing so on many occasions.
- The trailer has an extendible ramp that drops down and allows KITT to drive inside even when the truck is in motion.
- It is loaded with spare parts and equipment for KITT.
- It also has a computer lab where technicians Bonnie or April would work and conduct repairs and maintenance.
- At the front of the trailer is a small office area, a kitchen, and a sleeping area.
- In the fourth season, the Cab is outfitted with an autopilot feature and a TV so RC3 can watch his games while driving.
From Episodes 2 to 12, the trailer was plain white. The cab was just plain black. During this time period, only the first cab is seen with this version of the trailer and the semi is always stationary, never moving. From Episodes 13 onward, the trailer was painted black with gold striping and a Knight chess piece emblem on either side. The truck cab had gold striping added to it was well. All three cabs are seen pulling this version of the trailer. The semi is shown both stationary and moving from this point on as well.
For the entirety of the first season, the interior of the semi was very lab-ish looking. It has shelves with all of K.I.T.T.'s spare parts in crates, and a small work bench for Bonnie and two large computer consoles on the back wall. At the start of the second season, the interior was redone. The section were K.I.T.T. entered and exited remained mostly the same, with only schematics added to the side walls and two computer consoles added, one that drops down from the ceiling and one that is on wheels that sat on the side. The working area was redesigned to resemble more of a lounge. Wood paneling was added to the sides, and all the shelves became encased in cabinets. A sitting area was added, and another large computer console on the side, with the two still in the back. Over the course of the show, smaller amenities and equipment for K.I.T.T. were added and removed.
Three different trucks were used for the mobile unit. All three were GMC General tractor trailers.
- The first one used was a 1980 General with no sleeper compartment attached to it.
- The second one was a 1984 General with a sleeper compartment attached. The sleeper compartment had a more boxlike shape to it.
- The third was a 1984 General with a sleeper compartment attached. This sleeper compartment was more aerodynamic.
All three versions had a single-stack exhaust on the right side of the cab.
While the Mobile unit appeared in a majority of the episodes of the series as the mobile garage/HQ, it was featured as a plot device in a few episodes.
In the first season episode, Knight Moves, Michael uses the Mobile Unit to act as a decoy caring goods hoping that it will be hijacked. When the hijackers show up KITT exits from the rear and gives chase to the them, bringing an end to their hijackings.
In the second season premier, Goliath, Michael uses the Mobile Unit to trap Garth. K.I.T.T. locks Garth's steering wheel and is forced to drive up the ramp into the semi. Devon then places him under house arrest once in the semi. It is revealed here that the Mobile Unit has a roof hatch when Garth escapes through it.
In the third season episode, K.I.T.T. vs. K.A.R.R., K.A.R.R. turbo boosts into the Mobile Unit to gain access to circuits he needs to repair himself. This act destroys the rear ramp, and is assumed replaced after this episode.
In the fourth season episode, KITTnap, RC3 and Michael unhitch the trailer and take the cab to go and find K.I.T.T. after he has been stolen.
In the fourth season episode, The Wrong Crowd, a group of bikers hijack the Mobile Unit thinking it is the black liquor truck they are waiting for. They injure RC3 by pushing him from the cab. They make use of the computers in the trailer to try and get rich. Michael and K.I.T.T. are able to stop them just in time before they destroy the Mobile Unit with an armed solar powered robotic car they were trying to to steal to sell. The bikers flee and F.L.A.G. regains control of the semi.