The US has ordered 63 additional M777 howitzers from BAE Systems, taking the total order to 800 guns.
The new contract worth $118m allocates 38 guns for the US Army and Marines.
The remaining 25 are a part of the US foreign military sales programme for Canada, adding to their existing 12 already in service.
Final integration and test of the weapon system will be done at the BAE Systems global combat systems facility at Hattiesburg, Mississippi.
The weapon systems help the US and Canadian forces deployed in Afghanistan to provide fire support to the coalition forces.
The revolutionary M777 is the world's first artillery weapon to make widespread use of titanium and aluminium alloys, resulting in a howitzer half the weight of conventional 155mm systems.