A Light at the End of the Tunnel: Using an Improvised Laser Measuring System to Verify the Bore Dimensions of an XI-Inch Dahlgren Shell Gun

Abstract

ABSTRACT In developing a method to remove marine concretion from the bores of USS Monitor’s XI-Inch Dahlgren shell guns at The Mariners’ Museum and Park, a problem arose: how to determine the curve of the powder chamber to avoid damage during cleaning. Multiple period schematics showed conflicting dimensions, requiring direct measurement. An identical, non-archaeological XI-Inch Dahlgren from USS Kearsarge survives in Naval History and Heritage Command (NHHC) collections, creating the opportunity to verify the dimensions of an un-damaged analog of Monitor's guns. Measuring the Kearsarge Dahlgren represented its own set of challenges. A 3-dimensional laser scan would have been ideal, but neither the Museum nor the Navy’s lab possessed a scanner, and it was not financially viable to rent or purchase one. Even if free services could be found, the Kearsarge gun was in a secure military facility, complicating potential access for a third-party company. Instead, it was necessary to measure the gun’s bore with minimal expenditure. An improvised system was developed using a copy stand and a consumer-grade laser-measuring device. This system was transported to NHHC's storage facilities and successfully used to measure the Kearsarge Dahlgren’s bore, confirming the correct drawing and enabling further treatment of Monitor’s artillery.