The decision to build up a 5,000-strong armoured brigade in Lithuania over the coming years came in response to Russia's full-scale invasion of Ukraine in 2022.

The deployment is aimed at deterring potential Russian aggression towards Lithuania and fellow Baltic countries Estonia and Latvia, former Soviet states that have become NATO and EU members and fear they are increasingly in Moscow's crosshairs.

While Germany has joined multinational military missions, including in Afghanistan and Mali, a pacifist tradition stemming from its dark World War II history meant Berlin was generally reluctant to do more.

The establishment of a permanent brigade overseas is thus an unprecedented move for the Bundeswehr, as the German armed forces are known, in the post-war era.

Merz, who became chancellor this month, will participate in a ceremony in the capital Vilnius that officially marks the formation of the heavy combat unit, the 45th tank brigade, also known as the "Lithuania Brigade".

This will be an "important milestone on the path to the permanent stationing of a German brigade on NATO's eastern flank," deputy government spokesman Steffen Meyer said last week.

The brigade, to consist of around 4,800 troops and 200 civilian Bundeswehr employees, will be gradually deployed over the coming years and should reach full operational capability by 2027.

An advance party of around 400 Bundeswehr personnel are already in the country, according to the defence ministry.

- Bigger role -

Merz, who has vowed to build up Europe's "strongest conventional army" by ramping up defence spending, will be keen to use the trip to highlight that Berlin is taking on a bigger role on the international stage amid dizzying political upheavals.

US President Donald Trump has heaped pressure on fellow NATO members to increase defence spending, sparked fears about American commitment to Europe, and caused shock with his overtures to Russian President Vladimir Putin as he pushes for a swift Ukraine peace deal.

German Defence Minister Boris Pistorius, who will join Merz on the visit, said last month that the Lithuanian deployment "sends a strong message of solidarity and readiness".

"Germany is stepping up," he added during events to mark the 70th anniversary of Germany joining the 32-member NATO military alliance.

Merz is also due to meet Lithuanian President Gitanas Nauseda during his visit, with shared concern about Russia likely to dominate talks.

Lithuania, with a population of 2.8 million, borders both the Russian exclave of Kaliningrad and Moscow's ally Belarus, and the German defence ministry considers it to be "the most endangered state on NATO's eastern flank".

- Growing hostility -

There have been signs of Russia ramping up hostile activities, with Moscow frequently accused of using "hybrid warfare" tactics in the Baltic Sea.

Earlier this month a Russian spy plane was spotted in Belarus apparently attempting to observe a multinational NATO military exercise in Lithuania, news outlet Der Spiegel reported.

But Germany's troop deployment is not without its difficulties.

Some question whether the Bundeswehr, suffering from personnel and equipment shortages after years of underfunding, is prepared for what the defence ministry describes as "one of the most complex and ambitious projects" in its history.

While Germany has been seeking to channel more funds to the military, new equipment will take years to order and produce.

Meanwhile the Bundeswehr, which is aiming to boost its number of soldiers to 203,000 by 2031, has been struggling to recruit.

Parliament in January passed a law aimed at making the military a more attractive career, including more flexible working arrangements and greater financial incentives.