Officials from the Netherlands signed a letter of offer and acceptance to proceed with a $1.2 billion (€878 million) upgrade of the Dutch fleet of AH-64D Apache helicopters with the United States.

State Secretary of Defence for the Netherlands, Barbara Visser and U.S. Defense Security Cooperation Agency Principal Director for Security Assistance Michèle Hizon signed the letter at Gilze-Rijen Air Base on Friday, September 14, the DSCA said.

The agreement was first announced in February when the U.S. State Department approved the upgrade of 28 Dutch AH-64D Apache attack helicopters to the AH-64E configuration for an estimated cost of $1.191 billion. The principal contractors are Boeing and Lockheed Martin.

The Netherlands received its last Apache delivery in 2002 and the helicopters have become technically and operationally out of date after 20 years of service.

The first aircraft will be modernized beginning in 2021 and the first modernized Apaches will be reintroduced to the fleet by mid-2022, according to the U.S. Embassy in the Netherlands.

“Reinforcing the armed forces is in full swing. This contract signing is a good example of this. Our operations in Afghanistan, Iraq, and Mali have demonstrated the importance of Apaches,” Visser said on Friday. With this modernization our Apaches remain the versatile combat helicopters that our armed forces need.”

Also on Friday, Prime Minister Mark Rutte said the Netherlands would pull its F-16 fighter jets from the Islamic State mission in Iraq and Syria by the end of the year. A handful of Dutch special forces will stay in the country to continue training Iraqi forces, while a further 20 military and civil experts will remain part of NATO’s capacity-building mission in Iraq, which focuses “on the strengthening of the Iraqi security sector,” the government said.

In June, the Dutch defense ministry said that the Netherlands would end its troop contribution to the United Nations peacekeeping mission in Mali next May. Those troops will be sent to Afghanistan to “extend and intensify” the Dutch contribution to NATO’s Resolute Support mission, according to the ministry.