The subway system was constructed as a circular loop almost 6+1⁄2 miles (10.5 kilometres) long and extends both north and south of the River Clyde.

[3] Modernisation brought the installation of points and an access ramp between Govan and Ibrox where trains can exit the tunnel system for maintenance, cleaning or storage.

In the event of maintenance or repair work, the system can operate a full service (six trains per circle) with one of the sub-stations inoperative.

There was no additional cable to allow trains to reach the depot; instead, they were transferred to and from the running lines by crane operating over a pit at the Govan workshops.

[8]: 28  Late in the evening on the opening day, after 11 pm, one car laden with 60 passengers was run into by another under the River Clyde.

Anderson attributes this, and an increase in patronage in the years leading up to the conflict, to the expansion of the local shipyard workforce due to the need for rearmament.

[17] Unlike its larger counterpart in London the system's stations did not make good air-raid shelters as they were much less deep.

On 18 September 1940, during World War II, a German bomb, which dropped during a night raid on Glasgow and may have been intended for nearby naval facilities, landed on a bowling green to the south of Merkland Street station.

The resulting explosion caused damage to both tunnels, leading to closure of part of the system until repairs were completed in January 1941.

On 21 May 1977, the system was shut down eight days prematurely for a major refurbishment and modernisation; the date was brought forward because of the appearance of more cracks in the Govan Cross roof.

Badly deteriorated tunnels were repaired; stations were rebuilt and enlarged, with additional platforms at Buchanan Street, Partick, Govan, Ibrox, Hillhead and St Enoch.

The surface building of St George's Cross had already been rebuilt in 1971 as part of the construction of the Glasgow Inner Ring Road, and therefore was merely re-clad in the new corporate style.

Many fittings from Merkland Street were used to build a replica pre-modernisation station at the Glasgow Museum of Transport which contained three preserved cars.

[21] The modernised Subway (alongside the rebuilt Argyle Line) was inaugurated by Queen Elizabeth II on 1 November 1979, who rode the train along with Prince Philip from Buchanan Street to St Enoch.

Thirty-three new carriages were built by Metro-Cammell at its Washwood Heath works in Birmingham, and equipped with GEC electric motors.

[26] A £40,000 study examining the feasibility of an expansion into the city's south side was conducted in 2005, and in 2007 Labour further committed to extend the line to the East End, but to no avail.

In April 2010, Strathclyde Partnership for Transport approved outline plans for a £290 million upgrade of the Subway—the first since the comprehensive modernisation of the late 1970s.

[28] Plans included additional safety measures, improved accessibility and smart technology such as electronic tickets.

[29] The proposals were approved by the Scottish Government in March 2011, and changes to be brought in included: The first station to be modernised was Hillhead.

The work included the retiling of all the walls and floors, the replacement of escalators, a new ticket office, better way finding[clarification needed] and also a piece of public art.

Furthermore, all other stations were planned to receive updated branding prior to modernisation work being carried out on them, so as to achieve unity in design.

In March 2016, Strathclyde Partnership for Transport (SPT) awarded contracts to Stadler and Ansaldo STS for the supply of 17 new driverless trains for the Subway.

[39] The expansion of the existing network was also considered at a cost of £2.3 billion, including a new East End Circle, with seven new stations at St Mungo's, Onslow, Duke Street, Celtic Park, Dalmarnock, Newhall and Gorbals.

Other proposals include extending the system southwards to Cathcart and further westwards to the SEC Centre and Maryhill using an older railway line.

These links were improved at this modernisation: The first rolling stock was largely built in 1896,[45] with additional trailer carriages added over the following 20 years.

This rolling stock was converted from cable to electric traction in 1935 and finally withdrawn from service in 1977 upon the closure of the railway for modernisation.

[50] Strathclyde Partnership for Transport (SPT) unveiled a £200M contract with Stadler and Ansaldo STS in 2016 for modernisation of the Subway, including new driverless rolling stock.

[54] The concession fare is for disabled or elderly individuals who are holders of a National Entitlement Card that has been issued by SPT.

In September 2012 SPT launched an app for Apple iPhones and Android smartphones called iShoogle which allows users to "Check in" using Facebook at Subway stations.

It was popular as a stage piece performed by the comedians Rikki Fulton and Jack Milroy in their Francie and Josie act.