; and (2) 350 full-time support staff distributed among all United States ports of entry. (c) Air and marine operations Not later than September 30, 2021, the Commissioner of U.S. Customs and Border Protection shall hire, train, and assign sufficient agents for Air and Marine Operations of U.S. Customs and Border Protection to maintain not fewer than 1,675 full-time equivalent agents. (d) U.S. Customs and Border Protection K–9 units and handlers (1) K–9 units Not later than September 30, 2021, the Commissioner shall deploy not fewer than 300 new K–9 units, with supporting officers of U.S. Customs and Border Protection and other required staff, at land ports of entry and checkpoints, on the southern border and the northern border. (2) Use of canines The Commissioner shall prioritize the use of canines at the primary inspection lanes at land ports of entry and checkpoints. (e) U.S. Customs and Border Protection horseback units (1) Increase Not later than September 30, 2021, the Commissioner shall increase the number of horseback units, with supporting officers of U.S. Customs and Border Protection and other required staff, by not fewer than 100 officers and 50 horses for security patrol along the southern border. (2) Funding limitation Of the amounts authorized to be appropriated for U.S. Customs and Border Protection under this Act, not more than one percent may be used for the purchase of additional horses, the construction of new stables, maintenance and improvements of existing stables, and for feed, medicine, and other resources needed to maintain the health and well-being of the horses that serve in the horseback units. (f) U.S. Customs and Border Protection search trauma and rescue teams Not later than September 30, 2021, the Commissioner shall increase by not fewer than 50 the number of officers engaged in search and rescue activities along the southern border. (g) U.S. Customs and Border Protection tunnel detection and technology program Not later than September 30, 2021, the Commissioner shall increase by