Other
- Dahlgren gun, type of smooth bore cannon designed by the Admiral and used by the U.S. Navy
- Dahlgren Affair, failed mission to assassinate leaders of the Confederacy
- Dahlgren system and dahlgrenogram, created by Swedish-Danish botanist Rolf M. T. Dahlgren (1932–1987)
- USS Dahlgren (TB-9), Torpedo Boat No. 9/TB-9/Coast Torpedo Boat No. 4
- 6945 Dahlgren (1980 FZ3), Main-belt Asteroid discovered on March 16, 1980 by Lagerkvist, C.-I. at La Silla
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