1974 London pillar box bombings

On 25 and 27 November 1974 the Provisional Irish Republican Army (IRA) placed several bombs in pillar boxes and one in a hedge behind a pillar box. This was a new tactic used by the IRA in England, although a similar tactic had been used in Northern Ireland during The Troubles several times previously.

Source: Wikipedia — 1974 London pillar box bombings (CC BY-SA 4.0)