Randomizer

Escape of the Goeben - As First Lord he interfered directly in the deployments and actions of the two Admirals on the spot, Adm Milne, CinC Med and RAdm Troubridge SO 1 Cruiser Squadron. Due to confusing, poorly written and untimely orders directly from Churchill, Goeben was allowed to escape to Constantinople without being brought to action. Milne was cashiered (no great loss to the Navy but still...) and Troubridge was court-martialed for interpreting a poorly worded Churchill order regarding engaging superior forces in a manner the Churchill (and the Navy generally) did not like.
See The Ship that Changed the World by Dan van der Vat; and
Superior Force by Geoffery Miller.

Action off the Broad Fourteen's - Churchill directly interfered against the advice of the technical experts in the Admiralty Operations Division and ordered patrols off the Dutch coast using elderly armoured cruisers ill suited to the task in waters where U-Boat were known to operate. This after tasking the escorting destroyers to other duties.
See The Great war at Sea by Richard Hough; and
From Dreadnaught to Scapa Flow Vol II by Arthur Marder

Battle of Coronel - Again Churchill's micro-managing assets from the Admiralty and confusing orders placed RAdm Cradock in a position where he felt he had no choice but to fight a greatly superior East Asia Squadron. Amongst these were orders telling Cradock he was being reinforced by HMS Defence followed by new orders to Defence's captain to proceed elsewhere - without informing Cradock! By the time Cradock knew Defence was not joining he was already in the Pacific and committed to a fight, particularly as Troubridge's court-martial was pending.
See Coronel and the Falkland's by Geoffery Bennett, Hough and Marder.

The fleet action off the Dardinelles was Churchill's own creation. First Sea Lord Sir John Fisher wanted to strike Germany directly from the Baltic but Winston brought him around to the Dardinelles adventure and between them they convinced the War Cabinet. When the commander on the scene, VAdm Carden, who was ill but was very familier with the problems of the Straights objected, Churchill replaced him with RAdm de Roebeck, a compliant and unimaginative subordinate. Again through micro-management and poor instructions Churchill ensured that de Roebeck would be risk adverse rather than with boldness and decisiveness which was required if the operation was to have succeeded. Churchill also refused de Roebeck requested minesweeping experts from the North Sea which contributed to the losses on 18 March when Bouvet, Ocean, Irresistable and Inflexible were mined. Once his pet scheme to force the Straights using battleships collapsed he became the principle advocate of the amphibious operations at Gallipoli, again against the advice of many of his own technical advisors.
See Gallipoli by Allan Morehead, Hough and Marder.

When the war begin the Admiralty suspended the plan for using aircraft carriers for agressive anti-U-Boat patrolling. One of Churchill's first acts as First Lord was to reinstate these against the advice of the Director of Operations. They were suspended again after Courageous was torpedoed.
See The War at Sea by Stephen Roskill (a huge Churchill promoter)

Force Z was Churchill's baby from the start. His arrogant belief that two British capital ships would deter Japanese aggression was in spite of warnings from the Director of Naval Intelligence, Foriegn Office Asia Section and CinC Far East that this was not at all likely. When the fleet carrier allocated to Force Z, HMS Indomitable ran aground off Jamaica he did nothing to hold the squadron at Cape Town or Colombo until she was repaired, sending the obvious message to Adm Phillips that air cover was not required. The poor state of the RAF and the Army in Malaysia was the direct result of Churchill starving the Far east for resources to defend the home islands against the threat of an invasion that was over 16-months past.
See Battleship by Martin Middlebrook and Patrick Mahoney.

The Man at the Top bears responsibility for failure of an operation where he directly interfered with the chain of command or takes deliberate action to deprive the commander on the spot of necessary but available resources or issuing confusing, vague or restrictive orders that stifle initiative. Churchill was famous for both in how he would frequently run roughshod over senior officers, issuing orders directly to their subordinates and acting as though if he believed it to be so, it had to be true. For a man who's command of the English language was incredible, many of his written military and naval orders are models of chaotic thought, confusing, ambiguous and counter-productive.