Boeing will start building 13 more P-8A Poseidons under a $2.04 billion contract awarded on 31 July by the US Navy.
Deliveries from the fourth lot of low-rate initial production will raise the service's total fleet to 37 aircraft by the end of fiscal year 2016.
The USN plans to buy 117 of the 737-800-based maritime patrol and anti-submarine warfare aircraft to replace its current Lockheed P-3C Orions.
Boeing's contract also includes funds to buy long-lead parts to build 16 P-8As in the first lot of full-rate production, which is scheduled for award next year. The company says it has now received firm orders for 37 aircraft from the USN, and delivered 10 of these.