US Navy and Marines train for sea invasions at BaltOps 2019

When US Marines and sailors arrived in the Baltic region in June for 2019's Baltic Operations exercise, they did so as national leaders came together in Western Europe for the 75th anniversary of the D-Day landings.

But the 47th iteration of BaltOps wasn't tailored to that anniversary, said Navy Lt. Cmdr. Rob Sellin and Marine Maj. Jeff Starr, two officers tasked with planning amphibious operations for BaltOps 2019, in a June 2019 interview.

When they started planning in February 2019, they were aware of the timing, but the schedule was shaped by more immediate concerns. "This is the best weather time to be in this area of the world," Sellin said.

Sellin and Starr focused on big-picture planning and sought to get the most out of the exercises — "ensuring that we were able to include as many possible craft, as many ... landing craft on the amphibious side as possible," Starr said

"As we traveled and visited all these different countries and different landing locations," Starr added, "we really had an eye for the specific capabilities and limitations of all the craft that were going to be involved, so that we could make sure to get the maximum inclusion for our NATO partners and allies."

Below, you can see how the US and its partners trained for one of the most complex operations any military does, and how they did it in an increasingly tense part of the world.

US Navy Petty Officer 3rd Class Ty-Chon Montemoino briefs US and Spanish marines on boarding a landing craft utility while aboard the USS Fort McHenry.

(US Marine/Lance Cpl. Antonio Garcia)

Spanish amphibious assault vehicles prepare to exit the well deck of the amphibious dock landing ship USS Fort McHenry, June 15, 2019.

(US Navy/Mass Comm. Specialist 2nd Class Chris Roys)

US and Spanish Marines exit the well deck of the USS Fort McHenry on a landing craft utility, June 12, 2019.

(US Navy/Mass Comm. Specialist 2nd Class Chris Roys)

US and Romanian marines secure a beach after disembarking Polish mine layer/landing ship ORP Gnierzno, June 12, 2019.

(US Navy/Mass Comm. Specialist 3rd Class Jack D. Aistrup)

US Marines and sailors and Romanian and Spanish Marines secure a beach after disembarking from a Polish using Soviet Tracked Amphibious Transports and from Landing Craft Utility ships using Lighter Amphibious Resupply Cargo Vehicles and Medium Tactical Vehicle Replacements, June 12, 2019.

(US Navy/Mass Comm. Specialist 3rd Class Jack D. Aistrup)

Members of the US Navy Fleet Survey Team conduct a hydrographic beach survey in Ravlunda, Sweden, ahead of BALTOPS 2019, May 8, 2019.

(Naval Meteorology and Oceanography Command/Kaley Turfitt)

US Marines disembark a landing craft utility during a tactics exercise in Sweden, June 19, 2019.

(US Marine/Lance Cpl. Antonio Garcia)

US Marines exchange information with Spanish marines on the flight deck of the USS Fort McHenry, June 14, 2019.

(US Navy/Mass Comm Specialist 2nd Class Chris Roys)

US Marines and Romanian marines secure a beach after disembarking from Polish mine layer/landing ship ORP Gniezno in Estonia, June 12, 2019.

(US Marine Corps/Cpl. Abrey Liggins)

Royal Marines exit a British navy Merlin MK 4 helicopter via fast rope as part of an amphibious assault in Lithuania, June 16, 2019.

(US Navy/Mass Comm Specialist 3rd Class Jack D. Aistrup)

11 countries joined the BaltOps amphibious task group, and personnel from four countries took part in the landings. "Contrary to popular belief, the language barriers typically don't prove too concerning for these planning efforts," Starr said. "What does prove a little bit challenging for us is various communications systems and how they work interoperably."

Lithuania borders the Russian province of Kaliningrad along the Baltic Sea, placing some of the amphibious exercises close to Russia.

Spanish amphibious assault vehicles exit the well deck of the amphibious dock landing ship USS Fort McHenry, June 16, 2019.

(US Navy/Mass Comm Specialist 2nd Class Chris Roys)

A Polish PTS-M carries Romanian Marines ashore during an amphibious assault exercise at Baltic Operations 2019's Distinguished Visitors Day in Palanga, Lithuania, June 15, 2019.

(US Marine/Lance Cpl. Antonio Garcia)

Like other officials involved in BaltOps, Sellin and Starr stressed that the exercise wasn't directed at any other country. But tensions between Russia and NATO remain elevated after Moscow's 2014 annexation of Crimea — particularly around the Baltic states and the Russian exclave of Kaliningrad.

The Baltic states of Estonia, Latvia, and Lithuania are NATO members (and rely on NATO air forces to patrol their airspace) as is Norway.

Sweden and Finland are not in NATO but have responded to increasing tension in the region. Both have worked more closely with NATO in addition to bolstering their own militaries.

US Marines march to the beach from a landing craft utility for an amphibious assault exercise in Klaipeda, Lithuania, June 15, 2019.

(US Navy/Mass Comm Specialist 3rd Class Jack D. Aistrup)

A Royal Marine disembarks the USS Mount Whitney onto a landing craft vehicle attached to British Royal Navy ship HMS Albion in the Baltic Sea, June 16, 2019.

(US Navy/Mass Comm Specialist 2nd Class Scott Barnes)

Landing craft utility vessels stand by at sea after transporting Marines during an amphibious landing demonstration in Lithuania, June 16, 2019.

(US Marine Corps/Cpl. Tawanya Norwood)

Romanian Marines in an amphibious assault vehicle exit a landing craft utility as a part of an amphibious landing demonstration in Lithuania, June 16, 2019.

(US Marine Corps/Cpl. Tawanya Norwood)

US Marines perform a simulated amphibious assault from a landing craft utility in Lithuania, June 16, 2019.

(US Marine Corps/Cpl. Tawanya Norwood)

A US Marine and Spanish Marines buddy rush across the beach following an amphibious landing demonstration during the final event of NATO exercise Baltic Operations 2019 in Lithuania, June 16, 2019, June 16, 2019.

(US Marine Corps/Cpl. Tawanya Norwood)

A US Navy landing craft offloads vehicles during an amphibious exercise at Kallaste Beach in Estonia, June 12, 2019.

(US Navy/Mass Comm Specialist 3rd Class Jack D. Aistrup)

BaltOps 2019 took place just after the 75th anniversary of D-Day, and while that still colors popular perceptions of amphibious operations, Starr and Sellin said they don't plan for the kind of massive landing that put hundreds of thousands of Allied troops ashore in Normandy in 1944.

On June 6, 1944, more than 130,000 Allied troops rushed ashore on Normandy's beaches as part of Operation Overlord, the beginning of the assault known as D-Day.

Romanian Marines storm the beach during an amphibious assault exercise for Baltic Operations 2019's Distinguished Visitors Day in Palanga, Lithuania, June 15, 2019.

(US Marine Corps/Lance Cpl. Antonio Garcia)

US Marine Cpl. Timothy Moffitt runs ashore during an amphibious assault exercise for Baltic Operations 2019 in Palanga, Lithuania, June 15, 2019.

(US Marine Corps/Lance Cpl. Antonio Garcia)

"The reality is as amphibious planners, our job is to give our commanders a variety of options ... for ways to accomplish the mission, and it's very much not limited to putting a huge force ashore," Sellin said.

This article originally appeared on Business Insider. Follow @BusinessInsider on Twitter.