The Collaborative International Dictionary of English v.0.48:

Submersion \Sub*mer"sion\, n. [L. submersio: cf. F. submersion.]
   1. The act of submerging, or putting under water or other
      fluid, or of causing to be overflowed; the act of plunging
      under water, or of drowning.
      [1913 Webster]

   2. The state of being put under water or other fluid, or of
      being overflowed or drowned.
      [1913 Webster]

WordNet (r) 3.0 (2006):

submersion
    n 1: sinking until covered completely with water [syn:
         submergence, submerging, submersion, immersion]
    2: the act of wetting something by submerging it [syn:
       submersion, immersion, ducking, dousing]