structural:reformatting, information:extraction, information:filtering, structural:expansion
Blockade

When the war began, the French government ordered a blockade of the North German coasts, which the small North German Federal Navy with only five ironclads and various minor vessels could do little to oppose. For most of the war, the three largest German ironclads were out of service with engine troubles; only the turret ship SMS Arminius was available to conduct operations. By the time engine repairs had been completed, the French fleet had already departed. The blockade proved only partially successful due to crucial oversights by the planners in Paris. Reservists that were supposed to be at the ready in case of war, were working in the Newfoundland fisheries or in Scotland. Only part of the 470-ship French Navy put to sea on 24 July. Before long, the French navy ran short of coal, needing 200 short tons (180 t) per day and having a bunker capacity in the fleet of only 250 short tons (230 t). A blockade of Wilhelmshaven failed, and conflicting orders about operations in the Baltic Sea or a return to France made the French naval efforts futile. Spotting a blockade-runner became unwelcome because of the question du charbon; pursuit of Prussian ships quickly depleted the coal reserves of the French ships. But the main reason for the only partial success of the naval operation was the fear of the French command to risk political complications with Great Britain. This deterred the French command from trying to interrupt German trade under the British flag. Despite the limited measures of the blockade, it still created noticeable difficulties for German trade. "The actual captures of German ships were eighty in number".

To relieve pressure from the expected German attack into Alsace-Lorraine, Napoleon III and the French high command planned a seaborne invasion of northern Germany as soon as war began. The French expected the invasion to divert German troops and to encourage Denmark to join in the war, with its 50,000-strong army and the Royal Danish Navy. They discovered that Prussia had recently built defences around the big North German ports, including coastal artillery batteries with Krupp heavy artillery, which with a range of 4,000 yards (3,700 m), had double the range of French naval guns. The French Navy lacked the heavy guns to engage the coastal defences and the topography of the Prussian coast made a seaborne invasion of northern Germany impossible.

The French Marines intended for the invasion of northern Germany were dispatched to reinforce the French Army of Châlons and fell into captivity at Sedan along with Napoleon III. A shortage of officers, following the capture of most of the professional French army at the siege of Metz and at the Battle of Sedan, led to naval officers being sent from their ships to command hastily assembled reservists of the Garde Mobile. As the autumn storms of the North Sea forced the return of more of the French ships, the blockade of the north German ports diminished and in September 1870 the French navy abandoned the blockade for the winter. The rest of the navy retired to ports along the English Channel and remained in port for the rest of the war.