The hypothesis to test is internal gravity waves following a Garrett–Munk spectrum are sufficient to explain temporal coherence of sound at 3683 km in the Pacific Ocean for a signal at 75 Hz and a pulse resolution of 0.03 s. Signals from a 20 min transmission are collected on a towed array. After correcting the data for what likely appears to be acceleration of the receiver, the probability distribution for multipath coherence time is very similar to that obtained from Monte Carlo simulations of the impulse response. The most likely coherence time is 20 min, the longest that can be measured with a 20 min transmission. Predictions of multipath temporal coherence and amplitude fluctuations appear accurate enough to make useful predictions of channel capacity.