Battle of the Osfjord

The Battle of the Osfjord was an amphibious invasion and a battle of the Great War that resulted in a decisive victory in north to the Empire.

Background
From the beginning of the war against the Empire, the Entente Alliance took most of their national power to maintain the front line against the Imperial forces. Legadonia Army relied on the advantage of the terrain and climate to prevent their defense from breached for almost one and a half year. However, with the powerful voluntary forces in northern front been destroyed, the Imperial Northern Front had ensured sufficient military resources for a short-term offensive.

The Empire
In General Staff, von Zettour and von Rudersdorf, the Deputy Chief of Logistics and the Deputy Chief of Operations, reached a consensus to finish the Northern Front first. Considering the expansion work for the harbors and railroads in the Norden had already reached to the limit, any further increase of the load of supply transfer for the winter offensive will cause a heavy burden. In contrast, they had close to 300,000 tonnes of supplies to be shipped via sea. Hence, von Zettour suggested von Rudersdorf attack the enemy by an amphibious invasion instead of from land. He advised him to choose Osfjord as the landing site, because if they captured here, they would cut off the Legadonia's lines of supply and be able to use their railway system. To neutralize the coastal batteries of Osfjord, von Rudersdorf decided to send an elite mage battalion to the north.

On the other hand, the Imperial Northern Front were planning a massive offensive in winter. The materials necessary to supply the main offensive of Imperial Northern Front could be maintained about three weeks, which might be hard to break the enemies' resistance. However, the Imperial Northern Army had serious friction to the Imperial Central Army. The Northern Army picked up the pieces the General Staff had caused, such as disrupting their organization and taking many of their resources to the west. They were also taking much pressure from the other Fronts for how long they planned on dragging their campaign out. In that case, the General Staff had barely a position to have Northern Staff cease the short-term winter offensive, so they decided to accept their offensive and carry out an amphibious invasion as assist. The General Staff expected if this amphibious invasion succeeds, that will be a chance to rebuild the relationship with Imperial Northern Front, and Northern Army won't take the blame if it fails.

Legadonia Entente Alliance
The Legadonia Army was struggling against the Empire. Just fighting a Front of the Empire took most of their national power to maintain the front lines. They took some measures against sneak attacks to zones behind their front lines. So far, there were no major changes to the situation, because the Empire did not think the Entente Alliance was a threat, and was sparing minimal effort against them. The most serious event was a brigade of cavalry failing in their attempt to destroy their railway, or the airborne invasions conducted by a small group of mages. All these attacks were successfully repelled with haste by the Legadonia’s mage unit. Hence, they were confident in stopping the enemy’s attack if the invader’s numbers were limited. Nevertheless, after analyzing the result of the Dacian War, the Republic told the Entente Alliance that their defense of the territories to the rear were too weak, and that could be dangerous. In addition, the United Kingdom expressed concern over an attack by the Empire from the sea. However, the amount of capital ships their fleet had was two, which was difficult to defend their coast. Thus, they hoped the United Kingdom would keep watch over the movements of the Imperial navy, and if the need arose, the Republic’s fleet would attack immediately.

The Empire
On 29 November 1924, in the meeting of North Sea Fleet, the commander of the fleet informed the attendees about the details of this operation. Based on the plan, the first phase is the airborne invasion in the coastal fortress of Osfjord, carried out by 203rd Aerial Mage Battalion. They are supposed to neutralize the coastal batteries, torpedo launch positions, and the other things threaten the fleet before the dawn. Thirty minutes later, two marine mage regiment are supposed to arrive as the reinforcements, and the North Sea Fleet will approach the harbor of Osfjord to provide shore bombardment. Eventually, the marine corps will land from the ships, and marine mages will deal with the enemy reinforcements coming from the inland. When North Sea Fleet take off, High Sea Fleet are supposed to build the sea and air defense lines to keep the Republic Channel Fleet from North Sea Fleet. The General Staff got the information that beside the garrison, there was a new mage battalion that was just deployed, below strength, and usually lack of supply in Osfjord. It wasn't considered a threat. Finally, the operation was executed two days later.

Legadonia Entente Alliance
For the geographical importance, Os city is the primary connection point for their railway, and the coastal fortress of Osfjord was heavily guarded. Nevertheless, most army troops were in the front lines, any not many ones in the rear. In Col. Sue's opinion, their navy level wasn't quite different to the coast guard. Even a handful of their submarines were sent to join the regular ocean training before the war outbreak, and were thought of as war vessels by neutral countries, disarmed embarrassingly at last. In spite of the lack of naval strength, they still used some patrol boats to build a warning line in their coasts. They didn't know an amphibious invasion of the Empire was ongoing.

Invasion
At the night of Osfjord, 203rd Aerial Mage Battalion parachuted here from the transport aircraft. They started to capture or neutralize the coastal batteries. The 1st company is attacking Narva Battery, and 2nd company, Albert Battery. 3rd and 4th company are attacking the other threats. The Legadonia garrison found the regular communication of patrol boats lost, and a Legadonia mage battalion took off to fight with the Imperial mages. Later, two Imperial marine mage regiment arrived the Osfjord as the reinforcements, and the North Sea Fleet approached the harbor of Osfjord. The fleet provided shore bombardment, and protected the landing ships so that the marine corps can get on the port. Eventually, the Os city was captured by the Empire.

Aftermath
After Os city was captured, the logistic line of Entente Alliance Army was heavily disrupted, and lost the capability to defend the upcoming massive offensive of Imperial Northern Front. Afterwards, the Entente Alliance Army no longer had a chance to stop the march of the Imperial Army in north.

Reference
Plus Ultra - Chapter I Dacian War Plus Ultra - Chapter II Norden I Plus Ultra - Chapter III Norden II