The phenomena of underwater explosion and the damage mechanism due to explosion have already been investigated quite well by many researchers. It seems, however, to the author not yet being well discussed both the quantitative measurement of water pressures due to effects of expansion of successive gas globes and damage amounts. In order to make one part of these unknowns above explained clear, the experiment of cylindrical shells due to underwater explosion has been carried out, and these cylindrical shells were made of mild steel or high strength steel and stiffened by inner frames with different span lengths. After hanging the cylindrical shells by wire ropes at the depth of 30meters under the water on the about 1, 000meters depth sea, the explosion tests were pursued by blasting the TNT spherical explosives from either the bottom or side shell, yielding to the small and large damages on shells. This paper is mainly concerned with small local damages happened between frames, and hence the large ones were disregarded. Comparing both results of experiments and calculations on water pressures and displacements, the semi-empirical formulas of time lag among peak pressures due to gas globes and the amounts of maximum concavities of damages on the cylindrical shells were determined, and good coincidences were obtained between calculations and experimental results of the large cylindrical models of 5.5meters diameter made of mild steel, which were already carried out about 20years ago.