The transmission loss of an acoustic plane wave through a steel plate in water has been computed using Timoshenko–Mindlin plate theory and exact elasticity theory. Good agreement between the two models is found up to a frequency–thickness product of 20 kHz in. At 40 kHz in. and above, limitations of the plate theory approach become apparent.Subject Classification: [43]30.50; [43]20.60; [43]40.24; [43]20.30.