Otto Christian Hammer (18 August 1822 – 10 March 1892) was a Danish naval officer who participated in the First Schleswig War and the Second Schleswig War.
After a successful campaign along the west coast of the Duchy of Schleswig in the First Schleswig War, Hammer became a lighthouse inspector but quit service with the navy only a few years later.
When the Second Schleswig War broke out, Hammer enlisted again as an officer and lead a flotilla in the North Frisian Islands.
Despite an early success against Austro-Prussian forces he was later captured by a hostile expeditionary corps.
Retiring again from military duties, Hammer became involved in politics and established a lumber and fishery business in Sweden.
During that time he published his memoirs on the Second Schleswig War and also a text on fishery.