Transit (C) visas are nonimmigrant visas for persons traveling in immediate and continuous transit through the United States en route to another country, with few exceptions. Please find the complete information at https://travel.state.gov/content/travel/en/us-visas/other-visa-categories/transit.html and at https://ais.usvisa-info.com/en-ar/niv/information/visa_categories
Crewmember (D) visas are nonimmigrant visas for persons working on board commercial sea vessels or international airlines in the United States, providing services required for normal operation and intending to depart the United States on the same vessel or any other vessel within 29 days. If you travel to the United States to join the vessel you will work on, in addition to a crewmember (D) visa, you also need a transit (C-1) visa or a combination C-1/D visa.