This was the method the British military used to acquire soldiers or sailors for their ranks. For example, the Royal Navy would often board a foreign vessel and claim that members of the foreign crew were deserters of the Royal Navy and thus they were being taken back into British service. Whether or not the sailors were actually deserters of the British could not be proved, most often they were not. The British were "impressing" men into service of their military beyond their will. This recruting tactic became a problem for Americans in the early 1800s.
In 1803, after the shortlived Peace of Amiens, Napoleon Bonaparte declared war on England and the age-old battle for European supremacy once again took arms. Both sides, however, struck at neutral American trade in their efforts to strangle each other economically. Having gained command of the high seas after the Battle of Trafalgar, Britain was notorious for their impressment violations against foreign vessels.
The Royal Navy seized more than 500 American ships between 1803 and 1807, hovered off the US coast constantly creating a practical blockade, and impressed over 6,000 American seamen.
The issue of impressment by the British is a significant one because of the vehement response it elicited from the American people and government. The impressment also did an effective job enflaming Anti-British sentiment in America which contributed to the eruption of the War of 1812.
The British also impressed their own people into military service when needed. Military recruiters of the time were feared, as they often kidnapped derelicts, the poor, and homeless forcing them into service. Thankfully, the British and other nations eventually abandoned the practice of impressment to fill their ranks. The realization finally came about that it might be necessarily to actually pay and intice people to become enlisted members of the service, rather than forcing them into a form of military-sponsored slavery.