Question

Did the us ever join the coalition during the napoleonic wars

Answer 1

Basically US involvement in the Napoleonic War in alliance with France would end up with a similar situation to the War of 1812, especially when Napoleon invades Spain.

With the Royal Navy being Superior to the French and American Navies combined in the period of the Napoleonic war there would be little to no chance of French support reaching the Americans across the Atlantic and America would be too involved in fighting the British forces in North America to send that much aid to France...not to mention the fact that not every State in the Union wanted to fight Britain in the first place in the War of 1812 when it was a personal quarell between the two countries so I can't see them wanting to fight Britain just to help Napoleon.

With the Royal Navy able to depend on Horatio Nelson until Trafalgar (as that would probably happen regardless of the POD), Cuthbert Collingwood, Thomas Cochrane and William Sidney Smith (just to highlight some of calibre of the British naval commanders) it is unlikely that the tiny US Navy would be able to do anything against the British because in the War of 1812 they found it hard to even get out to sea so I find it hard to believe that they would be able to cross the Atlantic themselves.

In summary American involvement in the Napoleonic wars would just lead to two different fronts being created for the British, the Peninsular War and an American War, but I do not think that Britain would be unable to deal with that.