The calculation of the development of a spherical explosion in sea water, due to the symmetrical detonation of a charge of pentaerythritol tetranitrate, is carried up to the stage when the second blast wave converges as an implosive wave on the center and is reflected. Continuing earlier calculations by the authors, the complete field of disturbance is determined by the Eulerian approach, using the method of characteristics and boundary‐fitting techniques, up to the characteristic ray originating from the center at the time of implosion. At this ray the main shock has traveled approximately 7 charge radii from the center. The implosive phase of the second shock motion is a well‐known similarity phenomenon, and a variety of methods for treating this are discussed.