The St. Thomas Harbor is one of the most important commercial ports in the West Indies of the 1800s. The harbor was a free port. Traffic there was extensive because of its good situation & fine facilities.

It was popular among merchants & trading companies for its good facilities: the West Indies’ largest floating dock, good machine shops, clear channel marking, & inexpensive harbor fees. But it was also notorious for 2 problems: hurricanes & diseases, particularly yellow fever & cholera. In the 1800s, an average of 2,000–3,000 ships came annually to St. Thomas. In the 1860s, this increased to 4,600 annually.

About half of the tall ships arrived from Caribbean ports & a quarter from European ports. Vessels under the Danish flag made up a smaller share. In the 1820s, it was 23%; in the final year before the sale in 1917, it was only 13%. Most ships in the 1820s sailed under an American flag, but in the 1910s British ships had become completely dominant.

The vessels in the harbor became larger. In the 1st half of the 1800s, the average tonnage increased from 60 to 100 metric tons. From the 1820s to 1916, the total tonnage increased from 150,000 to 900,000 metric tons annually. In 1823, the first steamship ever put in to St. Thomas was a small North American steamer. From the 1860s onward, steamships came to the fore in earnest. In 1864 they accounted for 10% of the tonnage in the port.

In order to hold their own in international competition, extensive improvements were made to the harbor by the Danes at the start of the 1900s. The basin was deepened, wharves were constructed & conditions were generally improved. There were great expectations for the increased traffic that would pass the Danish colony on the way to & from the newly-opened Panama Canal. However, the outbreak of the First World War in 1914 frustrated all expectations, & the colony was sold to the USA in 1917.