As the latest zinger of the Obama Romney campaign has been that President Obama has somehow reduced the Navy to it's lowest level since 1917, it's appropriate to talk about the man himself who pushed for a robust Navy, Theodore Roosevelt.
TR was truly a Naval enthusiast, having authored a book on the history of Naval Warfare in the War of 1812 that was so well written it's still studied in the Navy today. In addition to writing a best selling book on the Navy, he also served as Assistent Secretary of the Navy under President McKinley where he constantly lobbied President McKinley for a more robust Navy and foreign policy.
He viewed America's failures in the War of 1812 as due in large part to the lack of a Navy that could stand up to British might. The British at the time were by far the largest and best Naval power in the world. It was their Navy that build the empire on which the sun never set. He felt the answer to avoiding military defeat in another potential invasion from a rival power was to drastically increase the number of ships in the United States Navy as well as professionalizing the maritime military forces.
It's not too surprising then that TR pushed a strong Navy in his budget when he came into office. The Navy was expanded from 59 ships before TR was the Secretary of Navy for McKinley in 1897 to 141 when McKinley left office in 1901. By the time TR left office as President in 1913, the Navy was up to 214 active ships.
By 1916 or 1917, the Navy ballooned to 342 active ships and then nearly doubled in the two years following. This is where the comparison loses meaning.
There are a few major factors to why Romney's argument that a lower active number of ships in the Navy means America is projecting an image of weakness.
The primary factor is that in the turn of the twentieth century, wars were fought very differently than they are now. For starters, there were no airplanes then. Navies were the primary vehicle of empire building and they could be used both offensively and defensively. The steam engine was invented, so the Navies also became much more reliable since they did not always need to also rely on good winds as the Navies have had to do in the past. Having a lot of ships roving the North and South American coastline deterred europeon invaders and were good tools to enforce America's interests in Latin America. Then as now, superior and more technologically advanced forces could easily win wars.