Radiation of sound from a submerged and freely flooded tube, closed at one end and open at the other, follows well‐known relationships if the exit dimension is much smaller than a wavelength. If the tube is instead filled with a gas and submerged in water, the radiated power is higher than that of the flooded tube for the same internal acoustic pressure. If the density‐sound‐speed product, ρc, is much higher in the liquid than in the gas, as would normally be the case, then the radiated power is greater by the factor 1/0.36(ka)2, wherekis the wave number in the water andais the tube radius. This provides an ideal setting for construction of an underwater acoustic source using a standing‐wave thermoacoustic driver since this driver is force limited rather than displacement limited. The performance is ultimately limited by the hydrostatic pressure and the dimensions of the tube.