The latest order is on top of the October 2009 purchase of 35 of M777A2 155mm howitzers, designated the M777 howitzer.
A joint statement by Minister for Defense Stephen Smith and Minister for Defense Materiel Jason Clare said the order for 19 of the towed M777 guns is a replacement for government's decision in May to cancel an order for self-propelled howitzers.
Smith and Clare said by having a single towed system and not having self-propelled types will allow savings in whole-life costs.
The additional howitzers will be purchased from production in the United States and avoids potential additional costs to restart such production in Australia, the statement said.
The government said it will consider additional support and facilities costs associated with the acquisition later in the 2012-13 financial year.
The M777 has a titanium and aluminium alloy structure able to fire up to five rounds per minute.
It is capable of being transported by Chinook helicopters and C130 aircraft.
A C-17 transport aircraft can carry a complete combat-ready system of howitzer, towing vehicle and crew transport vehicle.
The M777 is in service with the U.S. Army and Marine Corps. supporting U.S. operations in Afghanistan. The Australian purchase of more towed howitzers "strengthens interoperability with our alliance partner," the statement said.
The government also announced the roll-out within the coming year of 10,000 high-tech blast gauges to be worn by soldiers.
Minister for Defense Science and Personnel Warren Snowdon said the devices, developed by the United States Defense Research Projects Agency, measure the impact of blasts, particularly from improvised explosive devices.
Soldiers will wear three blast gauges -- on the outside of their helmet, on their non-firing shoulder and on their chest.
The gauges display a yellow, green or red light to indicate the level of pressure from a blast, Snowdon said.
The gauges, which weigh around 1 ounce, will help medics in Afghanistan treat injured soldiers by capturing blast data that can be used to determine the required medical treatment.
"The trial will enable medics to access data to immediately assess the effects of blast pressure and acceleration from an IED or other explosion on a soldier," Snowdon said.
"Bomb blasts can put enormous force and pressure on the brain. These devices measure that and help our medics treat our soldiers who have been hit."
The gauges are being rolled out by the Australian army's Diggerworks Team, which is responsible for developing combat solider capability and are similar to the United States Marine Corps. Gruntworks.
Snowdon said U.S. troops in Afghanistan also are trialling the gauges and have collected information from more than 250 blasts.
Snowdon first saw the gauges being worn by U.S. soldiers when he visited DARPA headquarters in Washington in 2011.