YOKOSUKA NAVAL BASE, Japan — U.S. sailors aboard the guided-missile destroyer USS McCampbell coached their Japanese counterparts Thursday as Japan prepares to receive its first shipments of Tomahawk cruise missiles sometime next year.

Around 25 Japanese sailors and airmen in the five-day program that ends Friday are the first round of students to learn the inner workings of the Tomahawks and their control systems. The training at Yokosuka, homeport of the 7th Fleet, is one milestone before the U.S. begins delivering the 400 Tomahawk missiles promised to Japan as part of a $2.35 billion deal.

“When the Tomahawks are delivered, we don’t start the training then,” U.S. Ambassador to Japan Rahm Emanuel told reporters aboard the McCampbell on Thursday. “We’re ahead of schedule because the delivery is going to be ahead of schedule.”

This week’s training is the first round, with additional rounds scheduled every two months, Emanuel said. Training will also likely continue after the missiles are delivered, he said.

“I expect the Japanese navy to do what our Navy officers do all the time, which is to be constantly training and upgrading skills,” he said the news conference.

Japan in 2022 announced plans to buy as many as 500 Tomahawks with delivery in fiscal years 2026 and 2027.

In October, the country’s Defense Ministry expressed a desire to fast-track the purchase. The Pentagon on Nov. 17 agreed to the deal, which includes 400 cruise missiles, 14 weapons systems, software, technical support and associated equipment. The first deliveries are expected sometime in fiscal 2025.

The purchase is part of a massive investment Japan has made into its defense. Japan’s Cabinet in December approved its largest-ever defense budget, which amounts to 7.95 trillion yen, or about $55.9 billion.

That investment, Emanuel said, is “100% in weapons and equipment” and is not an investment in more personnel or an attempt to increase the size of the Japan Self-Defense Force.

Emanuel said he is focused on completing the impending deliveries and could not comment on possible further sales.

“Before we even talk about more, we have a responsibility to get the first 400 and we’re on schedule to do that,” he said.

On Thursday, Japanese sailors and airmen worked studiously with U.S. sailors from the Surface Combat Systems Training Command Western Pacific in the McCampbell’s combat information center, the tactical heart of the ship. There, they participated in a simulated missile strike mission, according to Cmdr. Mike Arnold, the training command officer in charge.

“This was the cruise missile commander’s course,” Arnold told Stars and Stripes on Thursday on the McCampbell. The training, he added, covered overall capabilities of the missile, how to deal with casualties, tactics and how to “manipulate and execute the weapons system itself.”

Personnel from another six or seven commands were also in the training, according to Capt. Justin Harts, commodore of Destroyer Squadron 15.

“It gets to be sort of an alphabet soup of commands that are involved in any one of these operations,” he said. “And then there’s a whole host of commands in the States where the Japanese sailors are going to learn their individual jobs.”

The training is successfully increasing Japanese personnel’s capabilities with the missile and doing so “ensures a peaceful and stable Indo-Pacific region,” Cmdr. Yuhi Iwamori, spokesman for Japan’s Maritime Staff Office, told Stars and Stripes on Thursday.