The <a href="https://en.wikipedia.org/wiki/Operation_Big_Bang" id="mw2w" rel="mw:WikiLink" title="Operation Big Bang">Operation Big Bang</a>, the largest non-nuclear man-made explosion to that time, destroys bunkers and military installations on the North Sea island of Heligoland, Germany.<sup about="#mwt59" class="mw-ref reference" data-mw='{"name":"ref","attrs":{"name":"SpiegelHelgoland"},"body":{"id":"mw-reference-text-cite_note-SpiegelHelgoland-9"}}' id="cite_ref-SpiegelHelgoland_9-0" rel="dc:references" typeof="mw:Extension/ref"><a href="./April_18#cite_note-SpiegelHelgoland-9" id="mw3A" style="counter-reset: mw-Ref 9;"><span class="mw-reflink-text" id="mw3Q">[9]</span></a></sup>