Customs preventive control conditions departure on officer clearance after verification of formalities and financial compliance. Customs preventive control empowers officers to withhold port clearance until a written departure order is issued by the proper officer after verifying that prescribed formalities are completed and duties or penalties are paid or secured. Preventive Officers may board vessels and aircraft to obtain declarations and crew property lists, conduct selective rummaging and inspections based on vessel history, port of origin, and intelligence, and maintain surveillance to prevent unauthorized removals and unloading of unmanifested cargo.