The creeping attack was an anti submarine measure developed during the Battle of the Atlantic in World War II.
The problem addressed by Walker in the tactics then in use was that ASDIC, the active sonar means to search for and find a submerged submarine, searched forward, while the main weapon to attack it, the depth charge, was released or projected from the stern.
This led to a loss of contact in the final run up to target as the attacking ship passed over it, giving the U-boat a chance to move at the last minute and evade damage.
The more skilled or experienced U-boat commanders became adept at predicting the points at which the escort sped up to attack, and when they lost ASDIC contact, and were able to move aside while the charges sank to their depth.
The method required practice to get right, and was expensive of time and resources, but was devastatingly effective.