Heinz Guderian in the context of Nazi Regime

The Battle of Boulogne in 1940 was the defence of the port of Boulogne-sur-Mer by French, British and Belgian troops in the Battle of France during the Second World War. The battle was fought at the same time as the Siege of Calais, just before Operation Dynamo, the evacuation of the British Expeditionary Force (BEF) from Dunkirk. After the Franco-British counter-attack at the Battle of Arras on 21 May, German units were held ready to resist a resumption of the attack on 22 May. General der Panzertruppe (Lieutenant-General) Heinz Guderian, the commander of XIX Corps, protested that he wanted to rush north up the Channel coast to capture Boulogne, Calais and Dunkirk. An attack by part of XIX Corps was not ordered until 12:40 p.m. on 22 May, by which time the Allied troops at Boulogne had been reinforced from England by most of the 20th Guards Brigade.

The Guards had time to dig in around the port before the 2nd Panzer Division, which had been delayed by French troops at Samer, attacked the perimeter held by the Irish Guards at around 5:00 p.m. and were driven off after an hour of fighting. The Welsh Guards front was attacked at 8:00 p.m. and again at dusk, cutting off a party of the Irish at 10:00 p.m. At dawn on 23 May, the German attacks resumed, eventually pushing the defenders back into the town. About eighty light bombers of the Royal Air Force (RAF) flew sorties in support of the defenders of the port.

The Jagdpanzer IV / Sd.Kfz. 162, was a German tank destroyer based on the Panzer IV chassis and built in three main variants. As one of the casemate-style turretless Jagdpanzer (tank destroyer, literally "hunting tank") designs, it was developed against the wishes of Heinz Guderian, the inspector general of the Panzertruppen, as a replacement for the Sturmgeschütz III (StuG III). Guderian objected against the (in his eyes) needless diversion of resources from Panzer IV tank production, as the StuG III was still more than adequate for its role.

Officially, only the L/48-armed vehicle was named Jagdpanzer IV. The L/70-armed vehicle was named Panzer IV/70. In this article, both versions are referred to in general as Jagdpanzer IV, except in the variants and surviving vehicles section.

The siege of Calais (1940) was a battle for the port of Calais during the Battle of France. The siege was fought at the same time as the Battle of Boulogne, just before Operation Dynamo, the evacuation of the British Expeditionary Force (BEF) through Dunkirk. After the Franco-British counter-attack at the Battle of Arras (21 May), German units were held back to be ready to resist a resumption of the counter-attack on 22 May, despite the protests of General Heinz Guderian, the commander of the XIX Armee Korps, who wanted to rush north up the Channel coast to capture Boulogne, Calais and Dunkirk. An attack by part of the XIX Armee Korps was not authorised until 12:40 a.m. on the night of 21/22 May.

By the time the 10th Panzer Division was ready to attack Calais, the British 30th Infantry Brigade and 3rd Royal Tank Regiment (3rd RTR) had reinforced the French and British troops in the port. On 22 May, the British troops had established roadblocks outside the town and French rearguards skirmished with German armoured units, as they advanced towards Calais. British tanks and infantry had been ordered south to reinforce Boulogne but were too late. They then received orders to escort a food convoy to Dunkirk but found the road blocked by German troops. On 23 May, the British began to retire to the old Calais walls (built in the 1670s) and on 24 May, the siege began. The attacks by the 10th Panzer Division were mostly costly failures and by evening, the Germans reported that about half their tanks had been knocked out and a third of the infantry were casualties. The German attacks were supported by the Luftwaffe, while the Allied defenders were supported by their navies delivering supplies, evacuating wounded and bombarding German targets around the port.

The XIX Army Corps (German: XIX. Armeekorps) was an armored corps of the German Wehrmacht between 1 July 1939 and 16 November 1940, when the unit was renamed Panzer Group 2 (German: Panzergruppe 2) and later 2nd Panzer Army (German: 2. Panzerarmee). It took part in the Invasion of Poland and the Battle of France.

It was formed in Vienna on 1 July 1939, the same day as the 2nd Panzer Division, but was not assigned to any single military district. Commanded by General der Panzertruppe Heinz Guderian, it was stationed in Pomerania prior to taking part in the invasion of Poland. It was officially tasked with constructing fortifications in preparation for an attack from Polish forces, though in fact German preparations for the invasion were already well advanced. Subordinated within Army Group North (responsible for Poland's north-western Danzig Corridor region) and supplemented by the 3rd Panzer, 2nd Infantry, and 20th Infantry Divisions, XIX Army Corps was tasked to strike southwards towards the Vistula river and thereby prevent any eastwards retreat of Polish troops to its west. Operations began on 1 September 1939, beginning World War II in Europe. During the initial days of the Polish campaign, the XIX Army Corps captured the city of Pruszcz and a bridgehead east of the Brda river, inflicted massive casualties on the Polish Pomorska Cavalry Brigade (described by William L. Shirer as "sickening evidence of the carnage" and "symbolic of the brief Polish campaign"), prevented attempts by the Polish 9th Infantry Division and the Czersk Operational Group to recapture the Brda's east bank, was visited at the front by Adolf Hitler, Heinrich Himmler, and Erwin Rommel, and suffered casualties of 150 fatalities and 700 wounded. Moved to operating east of the Vistula in support of the 3rd Army's left flank after the Battle of Różan, they were positioned to join in attacking Warsaw from the north but were hampered by the slow progress of Army Group South. Von Bock instructed Guderian to set his sights onto Brest-Litovsk, deep in the Polish rear. Miscommunications with the infantry-based XXI Army Corps caused casualties and risked them being encircled by Polish forces. The Battle of Brest-Litovsk followed soon after, with XIX Army Corps troops slowed but emerging victorious. After the Soviet invasion of Poland, XIX Army Corps yielded control of the city to the Red Army, in line with the Molotov–Ribbentrop Pact, which they had unknowingly violated. XIX Army Corps then represented Germany in the subsequent German–Soviet military parade in Brest-Litovsk. The unit received several commendations after the Polish campaign ended on 6 October, with Guderian himself awarded the Knight's Cross of the Iron Cross on 27 October.