The air tanker modification can be carried out to either a DC-10-10 or DC-10-30 series and involves the addition of an external tank and associated systems and support structure.

The water or retardant is carried in three center-line belly tanks.
The tanks have internal baffles to prevent fluid shift (and consequent shift in center of gravity) while in flight, and sit with a 38.1-centimetre (15.0 in) ground clearance.
All three tanks can be filled simultaneously on the ground in eight minutes.
The retardant is gravity-fed out of the tanks, and the entire load can be dumped in eight seconds, although the actual drop rate is computer controlled by the flight crew in order to produce the desired retardant spread over the fire lines.
The aircraft is capable of applying a line of retardant  91.44 metres (300.0 ft) wide by 1.609 kilometres (1.000 mi) long.

The external retardant tanks are designed to be filled from  standard 76.2-millimetre (3.00 in) cam-lock couplings.
Utilizing one, two or three hoses,  the tanks can be filled as quickly as base loading capabilities permit,  typically 15–20 minutes.
The tanks are vented to atmosphere by a vent  system installed on top of each tank to allow sufficient air into and  out of the tanks during retardant drops and filling.
Accurate quantity gauges are part of the installation.

The number of drops it can make in a day is only limited by the time it takes to reload the aircraft with water/fire retardant and fuel, as well as its need for a proper landing field, which may well be a considerable distance from the fire.

Skeptics have argued that the DC-10s lack maneuverability.
 However, despite its size, field experience has proven the plane’s agility above all types of terrain and in all atmospheric conditions deemed suitable for fixed wing operations in a Fire Traffic Area (FTA).

Unlike most existing and proposed Large Air Tankers (LATs), the DC-10 arrives at a Fire Traffic Area weighing significantly less than its certified maximum gross takeoff weight (MGTOW).
This is principally due to the reduced fuel load carried on fire missions.

As a result:
The 10 is frequently dispatched at a takeoff weight 40% lighter than its certified MGTOW.

The 10 turns comfortably within the turn radii of smaller aircraft including Single Engine Air Tankers (SEAT) and lead planes.

The 10’s improved thrust to weight ratio significantly increases rate of climb, and greatly enhances safety margins in a failed engine scenario.

The 10 enjoys a wide margin above stall at typical drop speeds and weights, even with a full retardant load.

One drop from the aircraft is equivalent to 12 drops from a Grumman S-2 Tracker.
Initially, the aircraft was intended to be operated primarily in California, and the entire state was serviced from the plane's Victorville base at the Southern California Logistics Airport, but in 2007 Cal Fire began looking into setting up a second operations base at Sacramento McClellan Airport in Northern California.
10 Tanker Air Carrier announced in 2007 that a second aircraft would be converted to tanker usage for the 2008 fire season.
The air tanker modification can be carried out to either a DC-10-10 or DC-10-30 series and involves the addition of an external tank and associated systems and support structure.
The water or retardant is carried in three center-line belly tanks. The tanks have internal baffles to prevent fluid shift (and consequent shift in center of gravity) while in flight, and sit with a 38.1-centimetre (15.0 in) ground clearance. All three tanks can be filled simultaneously on the ground in eight minutes. The retardant is gravity-fed out of the tanks, and the entire load can be dumped in eight seconds, although the actual drop rate is computer controlled by the flight crew in order to produce the desired retardant spread over the fire lines. The aircraft is capable of applying a line of retardant  91.44 metres (300.0 ft) wide by 1.609 kilometres (1.000 mi) long.
The external retardant tanks are designed to be filled from  standard 76.2-millimetre (3.00 in) cam-lock couplings. Utilizing one, two or three hoses,  the tanks can be filled as quickly as base loading capabilities permit,  typically 15–20 minutes. The tanks are vented to atmosphere by a vent  system installed on top of each tank to allow sufficient air into and  out of the tanks during retardant drops and filling. Accurate quantity gauges are part of the installation.
The number of drops it can make in a day is only limited by the time it takes to reload the aircraft with water/fire retardant and fuel, as well as its need for a proper landing field, which may well be a considerable distance from the fire.
Skeptics have argued that the DC-10s lack maneuverability.  However, despite its size, field experience has proven the plane’s agility above all types of terrain and in all atmospheric conditions deemed suitable for fixed wing operations in a Fire Traffic Area (FTA).
Unlike most existing and proposed Large Air Tankers (LATs), the DC-10 arrives at a Fire Traffic Area weighing significantly less than its certified maximum gross takeoff weight (MGTOW). This is principally due to the reduced fuel load carried on fire missions.
As a result:
The 10 is frequently dispatched at a takeoff weight 40% lighter than its certified MGTOW.
The 10 turns comfortably within the turn radii of smaller aircraft including Single Engine Air Tankers (SEAT) and lead planes.
The 10’s improved thrust to weight ratio significantly increases rate of climb, and greatly enhances safety margins in a failed engine scenario.
The 10 enjoys a wide margin above stall at typical drop speeds and weights, even with a full retardant load.
One drop from the aircraft is equivalent to 12 drops from a Grumman S-2 Tracker. Initially, the aircraft was intended to be operated primarily in California, and the entire state was serviced from the plane's Victorville base at the Southern California Logistics Airport, but in 2007 Cal Fire began looking into setting up a second operations base at Sacramento McClellan Airport in Northern California. 10 Tanker Air Carrier announced in 2007 that a second aircraft would be converted to tanker usage for the 2008 fire season.
DC-10 Air Tanker