The deal was concluded on Monday by Poland's Donald Tusk and Sweden's Ulf Kristersson during a round of Polish-Swedish government talks.
It covers three A26-class vessels – also known as the Blekinge class – built by the Swedish defence firm Saab Kockums for Sweden's own navy.
Stockholm was chosen last November as Warsaw's partner for the submarine procurement programme, known as Orka, when the two governments signed an agreement paving the way for the project.
The new vessels will be powered by diesel-electric engines fitted with an air-independent propulsion system, which lets them remain underwater for several days without surfacing to recharge their batteries.
They are due to replace ORP Orzeł, an ageing vessel that is currently Poland's only submarine in active service.
The first A26 is expected to be delivered to Poland in 2030, with the other two following in subsequent years.
Earlier estimates put the total cost of the programme at around PLN 20 billion (EUR 4.66 billion).
As well as the vessels themselves, the contract covers a logistics package, support for their operation, crew training and the infrastructure needed to bring them into service.
It also includes provisions for industrial cooperation between the two countries.
'A common future'
Speaking at a news conference, Tusk called it a historic agreement of major importance for the two countries' defence ties.
He said Sweden was one of Poland's best partners in defence, and that cooperation in the Baltic had "qualitatively changed the security situation" there, despite Sweden's relatively recent NATO membership.
The two countries, he said, shared the same outlook on the region and remained determined to keep supporting Ukraine against Russian aggression.
Monday's deal, he added, was "one stage" of the partnership, not its conclusion, and he hoped the Orka programme would prove to be a step in a longer collaboration rather than its final result.
Kristersson said relations between Poland and Sweden were now "the best in history... deeper and stronger than ever before."
He noted that the two countries were NATO allies, EU partners and Baltic Sea neighbours, and that trade between them had doubled over the past decade.
"We have a common history, we have a common geography, we have a common Baltic Sea, but more importantly, we have a common future," he said, describing the submarine deal as a "milestone" that would add to "the great military strength of both our countries."
Training to begin in August
Poland's deputy prime minister and defence minister, Władysław Kosiniak-Kamysz, called it the most important deal in the history of the Polish navy, saying it would finally give the country the ability to operate effectively underwater.
He noted that the programme had been promised by successive defence ministers, prime ministers and presidents for 30 years without being completed, until now, and thanked everyone who had contributed.
He described the new vessels as the most modern submarines for use in the Baltic, able to support both naval and special forces operations, with "extraordinary capabilities," precision, and the ability to remain "invisible to our adversary."
Sweden's Defence Minister Pål Jonson called it "a historic day for Swedish-Polish relations."
He said the Orka deal, combined with what he called a "Baltic Pact", would put far more submarines in the Baltic Sea, benefiting both countries and stability across the wider NATO and Atlantic area.
Until the new vessels arrive, he said, Polish sailors needed to quickly build up their skills: an upgraded A17 submarine will be made available next year as a stop-gap measure, with Polish crews due to begin training in Sweden from August.
Jonson added that the partnership needed to work both ways, pointing to Sweden's purchase of Poland's Piorun air-defence systems and a separate agreement on rescue vessels, which he said would let both navies place joint orders for equipment in future.
He called the overall deal "a landmark moment in military relations" between Warsaw and Stockholm.
(ał)
Source: PAP