1916: For two years during World War I, the bells were silenced and the clock face darkened at night to prevent attack by German Zeppelins.[11]
1 September 1939: Although the bells continued to ring, the clock faces were darkened at night through World War II to prevent guiding Blitz pilots.[11]
3–4 June 1941: The clock stopped from 10:13 p.m. until 10:13 the following morning, after a workman repairing air raid damage to the clock face dropped a hammer into the works.[18]
1949: The clock slowed by four and a half minutes after a flock of starlings perched on the minute hand.[19]
New Year's Eve 1962: The clock slowed due to heavy snow and ice on the long hands, causing the pendulum to detach from the clockwork, as it is designed to do in such circumstances, to avoid serious damage elsewhere in the mechanism – the pendulum continuing to swing freely. Thus it chimed in the new year 10 minutes late.[20]
30 January 1965: The bells were silenced during the funeral of statesman and Prime Minister Winston Churchill.[21]
5 August 1976: First and only major breakdown. The air brake speed regulator of the chiming mechanism broke after more than 100 years of torsional fatigue, causing the fully wound 4-ton weight to spin the winding drum out of the movement, causing a large amount of damage. The Great Clock was shut down for a total of 26 days over nine months – it was reactivated on 9 May 1977; this was the longest break in operation since its construction. During this time BBC Radio 4 had to make do with the pips.[22] Although there were minor stoppages from 1977 to 2002 when the maintenance of the clock was carried out by the old firm of clockmakers Thwaites & Reed, these were often repaired within the permitted two-hour downtime and not recorded as stoppages. Prior to 1970 maintenance was carried out by the original firm of Dents and since 2002 by Parliamentary staff.