Promoted to lieutenant on August 1, 1862,[1] he commanded the gunboat Mount Washington[2] in joint Army-Navy operations on the Nansemond River, and played an important role in the capture of batteries at Hill's Point in April 1863.

[3] On 2 May 1864, at the New York Navy Yard, Lamson commissioned the gunboat Gettysburg, a former blockade runner captured off Wilmington, North Carolina, in November 1863.

He spent the next seven months commanding Gettysburg while stationed off the Cape Fear River, as part of the North Atlantic Blockading Squadron, capturing several ships.

[4] Lamson was in the forefront of the attacks on Fort Fisher, which stood at the entrance of the Cape Fear River protecting the approach to Wilmington.

The plan, concocted by General Benjamin F. Butler, called for the steamer Louisiana to be loaded with 215 tons of gunpowder and sailed under the walls of the fort and detonated, destroying the fortifications and stunning the garrison into submission.