Most names on the London Tube, or Underground, are either generic names like Metropolitan or District lines or geographical, like Circle, Piccaddilly, East London and Bakerloo or Northern lines. Even the Victoria line is named not after Queen Victoria but after Victoria Station, which it serves. The newest line, however, the Jubilee Line broke the mold.

Right , it doesn't correspond to any of Victoria's Jubilees or Elizabeth II's!

So what's the secret?

Don't know what is the secret, but the Jubilee line is certainly the nicest line in the London Underground!

Here's the supposed answer courtesy of Wikipedia:

The new line was to have been called the Fleet Line after the River Fleet, but the project was renamed for the occasion of Queen Elizabeth's 1977 Silver Jubilee and because the original plans to go west towards Fleet Street had been shelved. The original choice of battleship grey for the line's colour was based on the naval meaning of the word fleet, now transformed into silver.

The Jubilee Line was originally due to have been named Fleet Line because it follows the course of the underground River Fleet which also gives its name to Fleet Street. The name was changed to Jubilee Line to mark the silver jubilee of the queen in 1977. The Jubilee line from Baker Street to Charing Cross was built in the 1970s and incorporated the line from Stanmore to Baker Street which was part of the Bakerloo Line. When the Jubilee Line was extended from Green Park to Stratford, the line from Green Park to Charing Cross closed.

The line opened on 1 May 1979, taking over one of the Bakerloo Line's two branches to relieve congestion on their common portion. The Baker Street to Stanmore branch was joined to a new four-km segment into central London with a terminus at a new station at Charing Cross railway station. May 1 is the 121st day of the year in the Gregorian calendar (122nd in leap years). ... 1979 is a common year starting on Monday. ... The Bakerloo Line is a line of the London Underground, coloured brown on the Tube map. ... The northbound Bakerloo line platform. ... Stanmore tube station is a London Underground station at Stanmore. ... To help compare different orders of magnitude this page lists lengths between 1 km and 10 km (103 and 104 m). ... Charing Cross railway station. ...

The previous Charing Cross station, on the Circle, District, Bakerloo and Northern lines, was renamed Embankment. The new Charing Cross tube station created a new interchange, amalgamating the stations of Strand on the Northern Line and Trafalgar Square on the Bakerloo. This article is about a part of the London Underground. ... The District Line is a line of the London Underground, coloured green on the Tube map. ... The Bakerloo Line is a line of the London Underground, coloured brown on the Tube map. ... The Northern Line is a deep-level tube line of the London Underground, coloured black on the Tube map. ... Embankment Embankment tube station is a London Underground station in the City of Westminster. ... Charing Cross tube station of the London Underground serves both the Northern Line and Bakerloo Line networks and provides an interconnect with the national railway network at Charing Cross station. ... There have been two stations on the London Underground network called Strand station, both sites are located close to Strand. ... Charing Cross tube station of the London Underground serves both the Northern Line and Bakerloo Line networks and provides an interconnect with the national railway network at Charing Cross station. ...

The new line was to have been called the Fleet Line after the River Fleet, but the project was renamed for the occasion of Queen Elizabeth's 1977 Silver Jubilee and because the original plans to go west towards Fleet Street had been shelved. The original choice of battleship grey for the line's colour was based on the nval meaning of the word fleet, now transformed into silver. The River Fleet is the largest of Londons subterranean rivers. ... Her Majesty Queen Elizabeth II (Elizabeth Alexandra Mary Windsor), styled HM The Queen (born 21 April 1926) is the Queen regnant and head of state of Antigua and Barbuda, Australia, the Bahamas, Barbados, Belize, Canada, Grenada, Jamaica, New Zealand, Papua New Guinea, Saint Kitts and Nevis, Saint Lucia, Saint Vincent... 1977 was a common year starting on Saturday (the link is to a full 1977 calendar). ... Elizabeth IIs Silver Jubilee and her domestic and international visits proved very popular with her subjects. ... Fleet Street is a famous London street, traditionally the home of the press. ...

The Jubilee Line of 1979 was meant to be only the first phase of the project, but lack of funds meant the line stayed the same until the late 1990s. Phase 2 would have extended the line along Fleet Street to Aldwych and then across the River Thames to Lewisham. Events and trends The 1990s are generally classified as having moved slightly away from the more conservative 1980s, but keeping the same mind-set. ... Fleet Street is a famous London street, traditionally the home of the press. ... Aldwych tube station is a disused station on the Piccadilly Line of the London Underground. ... Length 346 km Elevation of the source 110 m Average discharge entering Oxford: 17. ... Categories: Docklands Light Railway stations | London railway stations | British railway stations | London Underground stubs ...

Changes in land use, particularly the urban renewal of the Docklands area, meant the project to extend the line beyond Charing Cross changed considerably in the 1990s. The Jubilee Line Extension, opened in three stages in 1999, split from the existing line at Green Park, creating a one-station branch to Charing Cross, which is now closed.

From a Jubilee Line googling attempt:

"During the Queen's Silver Jubilee year of 1977 the name was changed from "Fleet" to "Jubilee" for no particularly good reason."

Want to read more?
http://www.davros.org/rail/culg/jubilee.html

Geez, a lot of information got posted between 5:10 when I started my post and 5:20 when I finished. Sorry for the repetition.

And I can tell you that the majority of what you read above is DIRECTLY from Wikipedia or a similar source.

If they'd have called it Fleet line then strangers may think that it was the Fast line, which it is, the fastest in terms of speed by far on the Tube, even with automatic loading schemes in the newest appendage to prevent overcrowding - so not only fastest but most advanced technologically.