Joe Grasso & Son, Inc. (P) owns seven shrimp boats used for commercial shrimp fishing in the Gulf of Mexico. Each of the boats is operated by a captain and usually two crewmen. The employment taxes were assessed against P. P's sued for a refund. The United States brought a third-party complaint against the captains, alleging if P were able to put in issue facts proving that it was not the employer of the fishermen, then the same facts would demonstrate the liability of the captains for the taxes by showing an employer-employee relationship between the captains and the crewmen. The district court dismissed the third-party complaint. This appeal resulted.