; 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, 2023, the Commissioner 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 and not fewer than 264 Marine and Air Interdiction Agents for southern border air and maritime operations. (d) U.S. Customs and Border Protection K–9 units and handlers (1) K–9 units Not later than September 30, 2023, 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, 2023, 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) Horseback unit support The Commissioner shall construct new stables, maintain and improve existing stables, and provide other resources needed to maintain the health and well-being of the horses that serve in the horseback units of U.S. Customs and Border Protection. (f) U.S. Customs and Border Protection search trauma and rescue teams Not later than September 30, 2023, 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, 2023, the Commissioner shall increase by not fewer than 50 the number of officers assisting task forces and activities