Bern’s armaments director Martin Sonderegger and F-35 program manager Darko Savic signed the procurement contract on Monday, per a government release. The contract, worth 6.035 Swiss Francs (U.S. $6.25 billion) includes 36 of the conventional takeoff-and-landing aircraft variant, due to replace the nation’s fleets of F/A-18 Hornets and F-5 Tigers between 2027 and 2030. The Swiss parliament voted last week to green-light the procurement, which paved the way for the contract signatures.

Defense officials also signed an offset agreement with F-35 manufacturer Lockheed Martin, which “forms the basis for the U.S. manufacturer to conduct offset businesses with the Swiss industry,” per the government release. Swiss companies could receive contracts with a volume of about 2.9 billion Swiss Francs (U.S. $3 billion).

The first eight F-35As will be manufactured at Lockheed Martin’s facilities in Fort Worth, Texas, where they will also be used to provide initial training for the Swiss pilots, Bern announced in March. At least 24 subsequent aircraft will be manufactured and assembled by Leonardo at the Final Assembly and Check-Out (FACO) facility in Cameri, northern Italy.

Officials are still examining whether four aircraft could be assembled in Switzerland, at Ruag’s facilities, a Swiss government spokesperson told Defense News on Monday. If that is not possible, those four will also be manufactured in Cameri, the spokesperson said.

The Italian Air Force and Navy fly the F-35A and F-35B variants, respectively, built in Cameri, where the production line also services the F-35As for the Dutch Air Force.

The F-35 has increasingly enjoyed popularity in Europe over the past several years, as Switzerland is one of several nations to select the joint strike fighter to upgrade their fighters. The aircraft beat out other candidates including the Eurofighter Typhoon – built by a consortium comprising Italy’s Leonardo, the U.K.’s BAE Systems, and Airbus, which represents Spain and Germany – as well as Dassault’s Rafale and Boeing’s F/A-18E/F Super Hornet.

The Swiss government has been pushing to get the F-35 contract inked before the offer period ends next spring, amid efforts by the “Stop F-35″ coalition to schedule a popular referendum to block the sale. The coalition, made up of Swiss socialist and Green Party members, gathered over 100,000 signatures to launch a referendum campaign after the 2021 fighter aircraft selection, but Bern has consistently lobbied to move the deal forward despite the referendum demand. A Stop F-35 spokesperson expressed dismay at the contract signing in a Monday email to Defense News, and said that updates from the coalition will follow.

Lockheed Martin said in a Monday statement that the company is “honored the government of Switzerland is officially a part of the 5th Generation F-35 Lightning II program.”

“We look forward to growing the partnership with the Swiss Air Force and industry to deliver and sustain the aircraft for decades to come,” the company said.