Imperial German plans for invading the US

Those plans were made between 1897 and 1903, and were finally abandoned in 1906, when further threats in Europe (The formation of the Entente) forced Germany to play it's forces in the European continent.

Germany wanted a naval base in Cuba or Puerto Rico to control the Caribbean and then take the Panama Canal, thus having exclusive access to the Pacific.

The plans were shelved in 1906 and re-discovered in 2002 at the German military archive at Freiburg.

Plan I  

This plan was drafted by naval lieutenant Eberhard von Mantey back in 1898. The plan called for a major naval battle somewhere in the Atlantic in which the German Kaiserliche Marine would smash the American fleet and knock it out of the war temporarily. After that, the German Navy would bomb American shipyards, presumibly at Norfolk, Newport News and other places around Hampton Roads area, other potential targets were Portland, Maine; and the Portsmouth Shipyard at Kittery, Maine. The area around Hampton Roads was defended by Fort Monroe and Fort Wool, but everything east of Norfolk was virtually undefended.An attack on New York city was rejected due to the strong defences of the city.

After the American fleet was neglected, Germany would impose a naval blockade in the US and force the US government into German demands. Germany simply had not enough ships to carry on with this plan, and the subsequent Spanish-American War increased American influence over the Caribbean and the Pacific.

The Kaiser intended to expand the German Navy and ordered admirals Tirpitz and Diederichs to build a new high seas fleet.

Plan II

The Kaiser ordered von Mantey to revise the plan in March 1899. This time the Germans would carry a direct land assault in the US, landing forces in Boston and New York in a huge pincer maneuver. The invasion would recquire 60 warship, 40 to 60 cargo and troopships, 75,000 short tons of coal, 100,000 soldiers and would spend at least 25 days to cross the Atlantic.

Germany repeated the doctrine of defeating the US in a major and decisive naval battle (the same goal the Japanese aimed at WW2), then landing most of it's forces armed with artillery at Cape Cod, from there troops would advance into Boston and bomb the city from land and sea. In the New York front, Germans would land at Sandy Hooks Fort (NJ) and would send three infantry and one engineer batallions to take it, then the Germans would attack Fort Hamilton and Fort Tompkins, opening the way for Manhattan, which would be bombed by the Kaiserliche Marine to cause panic amongst the city's population and force the Americans into a truce.

Alfred von Schlieffen estimated that the US would accept peace if the Germans took atleast New York, a city which by the time had 3 million inhabitants, and qualified the plan as "unfeasible".

In 1899, Wilhelm II revised the plans and made it's own timetable. The whole fleet would set sail from Wilhelmshaven on the seventh day of mobilisation, then sail to the Azores in order to get coal and then reach the American East Coast on the 30th day. 

By 1900, the Kaiser changed his mind and decided that the absolute priority for the invasion was getting a land base in Cuba or Puerto Rico to use as an invasion base, a base which would have first to be taken by force, thus negating the German surprise attack on the US coast. By this time, the German Fleet had 38 battleships, 38 light cruisers, and 20 heavy cruisers.

Diederichs estimated that it wouls take 50,000 men to take Cuba and then 100,000 to take Boston, while the number of troops to take New York was simply impossible to supply.

In August 1901, lieutenant Hubert von Rebeur-Paschwitz spied the US east coast and detected several weak places from which the Germans could attack. He noticed that Cape Cod was not the best place to attack due to it's distance from the sea, and decided that the best places to land troops would be Provincetown (north of Montauk) and Rockport as a secondary target, while other troops would take Manomet Bay, however, the hills close to Manomet Bay would impede German forces to advance if American artillery was already placed, which seemed likely, given the Americans expected the Germans to attack Boston. Cape Ann, 64 kilometers norh of Boston, was also considered as a good landing place.

Plan III

This plan was drafted between 1902 and 1903 and Wilhelm Büschel, a naval officer, also took part in the planning. This time the German priority was having a naval base at the island of Culebra, Puerto Rico, before invading the United States. The plan is basically a reboot of Plan II.

The plans were finally cancelled due to a series of reasons, noteworthy: The Venezuelan crisis of 1903 in which the US sent most of it's navy (54 ships) to Venezuela in order to show it's naval force, the stablishment of the Entente Cordiale between France and Britain, the Russian negatives to ally with Germany, and the first appearing of Dreadnoughts in 1906.

Bibliography

https://en.wikipedia.org/wiki/Imperial_German_plans_for_the_invasion_of_the_United_States
https://io9.gizmodo.com/the-secret-german-scheme-to-invade-america-before-the-f-1628063060