The Type P or "Provisional" cancel type applied only to a government-issue cancel that has been modified by the mail clerk after it is received. The two most common forms of modifications are the addition of the ship's name to a 2z or 3z cancel, and changing or deleting part of the wording in the dial.

The following cancel is from the U.S.S. Electra (AK-21) and is classified as Type P [E-13]

As you can see, it is a Type 3z (BBT) cancel with the ship's name in the killer bars. The "[E-13]" tag indicates that this cancel type for this ship is shown as illustration "E-13" in the Catalog of United States Naval Postmarks (ISBN 0-9657316-0-X) published by the Universal Ship Cancellation Society.

The following cancel is from the U.S.S. Pennsylvania (BB-38) and is classified as Type P (U.S. Fleet Flagship 3t(*)) [P-15f]

As you can see, it is a Type 3t cancel with "U.S. Fleet Flagship" replacing the ship's name. The "(*)" indicates that the dial text includes a star. The "[P-15f]" tag indicates that this cancel type for this ship is shown as illustration "P-15f" in the Catalog of United States Naval Postmarks (ISBN 0-9657316-0-X) published by the Universal Ship Cancellation Society.

Locy System for Classifying Naval Postmarks, As Revised ©, of the Universal Ship Cancellation Society is excerpted and reprinted with permission.