Two sailors peered through binoculars from the bridge of the naval vessel as it patrolled the Irish Sea on a still morning in early May.

As they scanned the horizon, Lt. Cmdr. Maria O’Callaghan, the captain, pointed to a series of lines on a navigation display, indicating underwater power cables and gas pipelines that stretch between Ireland and Britain.

The crew of the Irish ship, the George Bernard Shaw, was looking for anything out of the ordinary while the captain used the screen to monitor a large vessel transporting liquefied natural gas. Although the ship was not on a sanctions list, the crew knew from tracking it in the past that it was heading north toward a Russian port, narrowly skirting Ireland’s territorial waters.

Their patrol was part of a stepped-up campaign by Ireland to apply greater scrutiny to the waters that surround it, as hybrid threats from an emboldened Moscow hang over Europe and ships seeking to circumvent Western sanctions sail in and out of Russia.

As America retreats from longstanding alliances in Europe, experts have warned that the small island nation, with permanent military forces of only 7,500, could be a weak link in European defense. That has resonated with the Irish government as it moves to modernize and bulk up its own defenses.

Lieutenant Commander O’Callaghan, 38, said her ship had begun hailing and questioning vessels over the radio at a level never seen in her 20 years of service. “It’s just about interrogating the information that is out there,” she said. “It’s mostly about looking at what’s around and being curious.”

Ireland has a long tradition of military neutrality, and successive Irish governments have used that posture to justify low defense spending. It is not a member of NATO, but Ireland carries outsize importance, security experts say, as a global data hub and as the European headquarters for many multinational technology giants, including Apple, Google and Meta.

Ireland’s foreign, trade and defense minister, Helen McEntee, said in an interview with The New York Times that her government was working swiftly to close a gap left by underinvestment.

“We need to be clear about what we as a country need to do, and that’s have stronger defense and security, that we need to invest in it more,” she said. “We are doing just that.”

The change is happening “as quickly as possible,” Ms. McEntee said, asserting that hybrid threats from Russia had made one thing clear: “Ireland is not immune to that.”

Ireland has raised its overall defense budget for the period from 2026 to 2030 to 1.7 billion euros, around $1.97 billion, a 55 percent increase. In February, it unveiled its first Maritime Security Strategy, setting out a five-year plan to protect its interests at sea and strengthen defense.

The maritime threats are growing, security experts agree. They cite the so-called shadow fleet, a group of aging tankers that covertly carry Russian fuel to avoid Western sanctions, but which are suspected of also sabotaging undersea cables elsewhere in Europe.

In 2024, the Yantar, which Western security services say was a Russian spy ship used to gather intelligence and map critical underwater infrastructure, was escorted by Ireland’s naval service out of Irish waters off the country’s west coast. It passed through the Irish Sea again in 2025. Other Russian vessels have been spotted lurking over data and energy cables in Irish waters.

A significant number of shadow fleet vessels ships have routed around Ireland’s west coast in recent weeks after Britain announced a new policy allowing the Royal Navy to board Russian ships under sanction transiting through its waters.

Because of legal and capacity limitations, there is little more the naval service can do than radio other ships and ask questions. Ireland lacks subsea sonar, anti-drone and air defense capabilities across its eight-vessel fleet. Crew shortages have also stymied patrols.

“Ireland certainly has a very steep hill to climb,” said Mark Mellett, a former chief of staff of the Irish Defense Forces, adding, “For Russia to get stronger, all that has to happen is for Europe to look weaker.”

The concerns feel more urgent this summer as Ireland prepares to host the rotating presidency of the European Union for the second half of this year. That will bring European leaders to the island for a series of meetings that pose potential security risks. In 2025, for example, Denmark reported drone incursions into its airspace while it held the position.

Ireland also wants to show a greater commitment to its European partners as it prepares. The government has accelerated some defense plans, including a military radar program. Some counter-drone technology will be introduced in the coming weeks. Officials also point to the budget increase over five years as a sign of greater commitment.

Others worry that the measures do not go far enough fast enough.

Barry Andrews, an Irish member of European Parliament, in a report earlier this year, found that Ireland’s security governance, infrastructure and military capabilities were not sufficient in the current security climate. While he acknowledged that some progress had been made, he said the upcoming presidency raised particular concerns.

“That puts a target on your back, and countries with far more sophisticated defense capabilities suffered major interruptions to their infrastructure during their presidency,” he said in an interview.

“I think the threat situation for Ireland has changed in the last few years because of major issues beyond our borders,” he said, citing America’s waning commitment to NATO under President Trump, as well as Russian aggression in Ukraine. “Also, Ireland had sort of a practice of strategic helplessness for a long time. And the U.S. and NATO and the U.K., they looked after the Irish defense and security, implicitly.”

Ireland’s military neutrality, a cornerstone of its foreign policy, has a long, complex history, rooted in hundreds of years of British occupation of the island, and the subsequent war of independence and civil war.

Since the state’s founding, it has maintained military neutrality, including during World War II.

The notion has stayed popular, and Ms. McEntee, the defense minister, dismissed the idea that the government was shedding that stance.

“Ireland’s position of military neutrality is not a position that’s in question,” Ms. McEntee said, but added that neutrality didn’t mean the country shouldn’t invest in defense.

The country also has longstanding involvement in peacekeeping missions, a point of national pride. Ireland sends its largest number of troops to the U.N. peacekeeping mission in Lebanon, known as UNIFIL.

Ireland has plans to increase its permanent defense personnel to 11,500 by 2028. And the naval service — long tasked with duties like policing fishing grounds, intercepting drug smugglers and search and rescue — will soon begin an upgrade that will modernize vessels and enhance recruitment.

The shifts in the security climate will be “taking us on a path where we have never been before,” said Aonghus Ó Neachtain, a naval service press officer, noting that Ireland had gone from monitoring around four shadow fleet vessels in its waters at any one time to something like three dozen in recent weeks. “We just didn’t foresee a lot of these things happening,” he added.

For Lieutenant Commander O’Callaghan, the captain of the George Bernard Shaw, the view from the bridge will look very different in the coming months and years, with sophisticated sonar equipment alerting the crew to underwater activity and surveillance radar allowing them to track aerial threats.

It’s part of a rapidly changing awareness of the significance of the marine domain, she said, as the Bernard Shaw glided across a remarkably still stretch of the Irish Sea northeast of Dublin.

“You will hear it referred to as ‘sea-blindness’ — as a nation, we just didn’t understand, we were very much inward-looking,” she said. “But there has definitely been a shift in that.”