Jefferies tube On Starfleet vessel s , Jefferies tubes are internal maintenance conduits that are used to provide crew access to various ship ' s systems . In emergencies , they are also used for moving around the ship if turbolift s are not functional . Door s within the Jefferies tubes can be sealed for safety or security reasons . On all ship displays of internal structure , Jefferies tubes are not displayed , and in some cases show no sign where they could actually fit within the ship . 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 " . ( ) Jefferies tubes could also be used for fitness training exercises . ( ) Geordi La Forge sarcastically remarked that starship designers consider Jefferies tubes " easy access . " ( ) 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 crew members 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 nacelle s . 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 single functions like the tubes which were only designated engineering circuit bay s . 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 . Other horizontal tubes were still cramped , but crewmen could still walk freely up straight in posture . 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 . In 2374 , The Doctor sent the EMH Mark II to Jefferies tube 17 aboard the to release a neurozine gas . The EMH Mark II never accessed a Jefferies tube and The Doctor told him that , traditionally , such a Jefferies tube is 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 . ( ) Alien variant . On several alien starships , similar tunnels and tubes were used , known as crawlways and access tubes . Aboard the Vulcan combat cruiser " Seleya " , they were known as crawlways . ( ) Appendices . Background information . The 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 " . ( ) The name " Jefferies tube " was originally an in - joke , already in use during the production of " The Original Series " , but only came to be canon ically 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 ! " " ( " " , 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 Sona Tube that we cut and expanded a little bit . Sona Tubes 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 that allowed three people to climb simultaneously . This was no doubt convenient during red alert when crewmen needed to get to battle stations quickly . Unfortunately , this concept was never expanded upon , so we never saw a four - or even a six - sided hexagon - shaped ladder . Instead , the ladders in the Jefferies tubes of the 24th century were only capable of supporting one individual . 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 .