Jefferies tube
A Jefferies tube, also known as a service crawlway or service duct was a type of access tunnel or internal maintenance conduit that was used to provide crew access to various ship's systems. In emergencies, they were also used for moving around the ship if turbolifts are not functional. Doors within the Jefferies tubes could be sealed for safety or security reasons. 

During the 22nd and 23rd centuries, Jefferies tubes were usually referred to as access tubes, access tunnels, or service chutes, although the term was in use as early as 2256. () In the 24th century, the single term was generally favored, though some officers referred to them as "service crawl-ways". () Geordi La Forge sarcastically remarked that starship designers consider Jefferies tubes "easy access." ()
 
Jefferies tubes could also be used for fitness training exercises. ()

22nd century 

During the 22nd century, starships were outfitted with long and small service tunnels, which would later be known as Jefferies tubes. These were hard, cold, cramped, and poorly lit. Tunnels on some ships joined at a variable gravity "sweet spot". ()

Vertical tubes 
NX-class ships had vertical tubes to help their crew manually reach decks above them or below them. These tubes were circular from one end to the other. Each tube was equipped with a single one-way ladder for crewmen to climb or descend. The ladders had dim lights behind them so the crew could see where to step. ()

In September 2152, several crewmembers used these vertical access tunnels for transporting equipment and personal things to the catwalk. ()

Horizontal tubes 

The horizontal tunnels were not very different from the vertical ones. They were also circular and narrow. Crewmen had to bend their knees and crouch down at a bent posture while walking inside these specific tubes. A majority of the tube's space was filled with long and thick engineering pipes that went from one end to the other. These tubes were lit from the floor so a person could follow a path. (, et al.)

23rd century 

In the 23rd century, Jefferies tubes were still round and small, but they were better lit by that time and no longer simply a means to get around. They served many different functions and purposes. It was not uncommon to find many technicians and engineers tinkering inside them.

Diagonal tubes 

Many diagonal tubes were scattered all throughout starships. These tubes were always densely connected with important system controls, relays, various conduits, and vital engineering circuits. Some of these tubes led to crawl-way junctions, while some even continued on inside a nacelle pylon to one of the ship's actual warp nacelles. At the entrance of each tube were two red bars so a crewman could pull him or herself inside. A soft, yet strong light was always emitted from the top and filled the entire tube. Certain tubes had multiple functions, while others had a single function like the tubes which were only designated engineering circuit bays. Each diagonal tube was equipped with stairs for crewmen to walk up or down. (; )

Vertical tubes 

The vertical tubes on a starship, also known as gangways, allowed manual access to decks both above and below. These particular tubes were easily accessible in the open hallway alcoves located on every deck. On the walls of these tubes, there was a reflective material that perfectly illuminated the entire tunnel. The tubes were equipped with a single "three-way ladder" to allow more than one crewman to climb or descend. ()

In 2258 of the alternate reality, a ladder was visible aboard the  when  walked down a corridor after being relieved of duty as acting captain. ()

Horizontal tubes 

The horizontal crawl-ways on starships allowed manual access to various parts of a starship. These tubes were also densely connected with important system controls and vital engineering circuits. Some of these tubes even led to the matter-antimatter reaction chamber. Every few feet, a bright light could be found, shining down. Crewmen usually had to crawl while traveling in some of them due to the cramped size. ()

The Jefferies tubes aboard  vessels were dark in color and not well lit; unlike those in contemporary  vessels.()

By the 2280s, the horizontal tubes were still cramped but tall enough to allow crewmen to walk standing up.  Also by this time, they had become extremely well-lit. This was especially true late in the 23rd century. Late in that century, the horizontal tubes were extremely well lit, with lights coming from both above and below. ()

Tube junctions 

On a starship, the Jefferies tubes had junction service crawl-ways. They served as interconnected points linking all the different tubes. On  vessels, these junctions also gave access to critical starship systems, like plasma flow regulators and warp and power relays. ()

24th century 

During the 24th century, Jefferies tubes became more simple, less intricate, and not as thoroughly filled with vital systems.

Vertical tubes 

The vertical tubes on starships allowed manual access to decks both above and below, which were labeled inside these particular tubes. Dim lights were located behind the main ladder and other lights were found on every deck. These tubes were equipped with a single one-way ladder for crewmen to climb or descend. (; ; )

Horizontal tubes 
The horizontal crawlways on starships allowed manual access to various vital parts of a ship or station. Dim lights were located near the floor and on each side of the tube. Crewmen usually had to crawl while traveling in them due to the cramped size. Inside these tubes were removable panels to important system conduits and engineering controls. (; ; )

Certain horizontal Jeffries tubes on Galaxy class starships were full-height service corridors tall enough to walk comfortably in. These tubes had ladder-access to other decks. ()

In 2374, The Doctor sent the EMH Mark II to Jefferies tube 17 aboard the  to release a neurozine gas. The EMH Mark II had never accessed a Jefferies tube and The Doctor told him that, traditionally, such a Jefferies tube was accessed head first. ()

The same year, an explosion blew off a hatch and exposed Jefferies tube 84 aboard the  to space. ()

Tube junctions 

On 24th-century starships, all Jefferies tubes had junction service rooms. They served as interconnected points, linking all the different tubes. Every room had exposed conduits on the walls, sometimes with panels to access various power conduits or relays.

According to Nella Daren, the fourth intersect of Jefferies tube twenty-five was the most acoustically perfect spot on the . ()

Appendices

Appearances 
This is a list of Jefferies tube appearances, which were typically only seen on Starfleet/Federation vessels. For a list of tunnels seen on space stations and other vessels, see access tunnel.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  (Dax is seen in a Jefferies tube briefly before getting stuck in the turbolift)
  (Jefferies tube of the mirror universe )
  
  (Sisko steps out of a Jefferies tube and the tube is seen briefly)

Background information 

In universe, Jefferies tubes were probably named in honor of the 22nd century Starfleet engineer W.M. Jefferies. In reality, this character was named after Matt Jefferies, the designer of the original  and the Art Director of Star Trek: The Original Series. ()

The name "Jefferies tube" was originally an in-joke, already in use during the production of The Original Series, but only came to be canonically mentioned on a number of occasions in the later  television series, the first time being in that show's third season episode . Jefferies himself had indicated, "Somebody hung the name Jefferies Tube on it. It wasn't me, but the name stuck and I used it in some of my sketches!" (Star Trek: The Original Series Sketchbook, p. 72; ) The first recorded use of the nomenclature was a "SHOT – JEFFERIES TUBE" script reference in the draft of  of  (scene 36, p. 21, where the body of Gav was stashed), though it was not heard in the episode. Set Designer John Jefferies, the younger brother of Matt and who, with his team, had to build his brother's design, recalled the construction of the Original Series Jefferies tube: "It was the only part of that set that was moved on [note: meaning it was a mobile set, mounted on rollers] that was on an incline, and it was made out of a Sonotube that we cut and expanded a little bit. Sonotubes were large cardboard tubes that could be purchased. They were used for forming concrete and we would buy these in either eight- or ten-foot lengths and they came in many varying diameters. They ran about a half an inch thick and they were wrapped cardboard. Well, we found these marvelous for pieces of set and curved walls, because they were quick." ("Designing the Final Frontier", TOS Season 2 DVD special features)

The access tubes have changed appearance many times in the past fifty years, while still maintaining their basic function for both the series and films. The tubes were commonly used as a last-minute deus ex machina, whether it was a relay circuit inside that needed to be repaired, or a straightforward means of physical escape.

The most unusual variation of the Jefferies tube was a vertical tube shown in the original Star Trek series. This access tube had a "three-way" ladder (arranged in a triangular prism) that allowed three people to climb simultaneously. This was no doubt convenient during red alert when crewmen needed to get to battle stations quickly. This concept was not adopted for later series. Instead, the ladders in the Jefferies tubes of the 24th century were standard "single" ladders.

An in-joke reportedly appearing in the Jefferies tube sets on the original Star Trek series (although written so small as to be invisible to the audience) were labels on pipes, marked "GNDN". This stands for "Goes Nowhere, Does Nothing". The marking also appeared on various sets for the .

Traditionally, Jefferies tubes were cramped crawling spaces, but in , a particularly spacious one was featured. Commenting on this large Jefferies tube, Star Trek archivist Penny Juday explained (in ), "The Jefferies tube is used even today [....] So, Herman Zimmerman has made sure that the name sticks [....] Almost all the time – not in every episode of course – but when we need a crawl space, that's exactly what we use; it's always called a Jefferies tube.''" ("Designing the Final Frontier", TOS Season 2 DVD special features) The canonization of the term "Jefferies tube", however, fell to Zimmerman's successor, Richard James, to implement in the aforementioned episode "The Hunted". Chronologically, the reference in  establishes it to have been referred to in that way as early as 2256.

See also 
 Access tunnel
 Catwalk
 Emergency access conduit
 Maintenance shaft

External links 
 
 

cs:Jefferiesův průlez
de:Jefferies-Röhre
fr:Tube de Jefferies
Spacecraft sections