The owner of any truck who secured and paid for a license therefor but was prevented from operating the truck for the full license year by induction into the armed forces of the United States and who, after his discharge from the service, resumes his trucking operations, shall be entitled to a pro rata credit on any new license purchased by him, in the proportion that the part of the year for which he had paid the license and during which part the truck was not in operation bears to the full license year. The application for a credit shall be made during the license year for which credit is sought and each application shall be accompanied by the registration card and license plate issued the owner for the year for which credit is sought and an affidavit that the owner has been or will be inducted into the armed forces. All such affidavits shall set forth that the vehicle cannot be operated due to the owner’s service in the armed forces. The Commissioner, when the owner is entitled to a refund, shall issue to him a credit to be applied on the purchase of a new license, in the proportion that the part of the year for which the license fee was paid and during which the truck will not be operated bears to the full license year.