On April 11, Klingenberg's instructions were to reconnoiter and establish checkpoints, secure any bridges and roads encountered, then hold for reinforcements. Heavy rains and melting snow had washed away nearly all soft surfaces, and bridges had been destroyed by retreating Yugoslav forces. The main avenues of approach to Belgrade were no longer viable routes, and the tanks would be hard pressed to continue without massive engineering support to clear those areas. After several hours of observing the stricken city from across the Danube River, Klingenberg believed that Belgrade was his for the taking, due to the confusion caused by the bombardments -- provided his unit arrived in time. He had only 24 hours to submit a report to his command, and a decision had to be made quickly.
Klingenberg saw a chance to probe more deeply into the city's environs when one of his men found an abandoned motorboat tied to a tree along the banks of the swollen Danube. Taking only one sergeant and five privates, he negotiated the treacherous river. The trip was extremely dangerous, the currents raging from the runoff of melting snow in the mountains and from torrential rains. The boat was overloaded, as well. Reaching the far side of the Danube, Klingenberg sent two men back to ferry more troops over before sunset. On the return trip, however the boat struck a submerged obstacle and sank. Klingenberg's "navy" ceased to exist, leaving the captain and six of his men stranded. They were totally isolated, with limited supplies and ammunition.
The squad advanced along the road and encountered a few British-made vehicles manned by Yugoslav soldiers. They captured two trucks and a bus, along with some 20 enemy soldiers. One of the men on the bus was an inebriated German tourist who had been trapped in Belgrade since the invasion started. The tourist, who spoke Croatian, had been apprehended as a spy by the Yugoslav soldiers and was being taken to be executed. He was still drunk and unaware of his impending fate. When he sobered up, he thought that he was still among his group of partygoers until he was informed of the situation. Klingenberg used him as an interpreter, in which capacity the grateful German was most helpful.
The SS men continued on, using their prisoners and a few captured uniforms to get past several enemy checkpoints. They made good progress the first day without any of the enemy checkpoint guards becoming suspicious. The Germans added the Yugoslav guards to the increasing number of prisoners they were collecting along the way. The population of Belgrade, after several days of bombing, was anticipating a long siege rather than an attack, and the lax security that Klingenberg encountered played directly into his hands.
Upon entering the outskirts of the city, the Germans became involved in a two-hour running firefight. They finally drove their captured vehicles into the city with many wounded prisoners aboard, including the hapless tourist. Miraculously, none of the SS men were wounded in the fight. They ended up in the city center, all alone and surrounded by a wide-eyed, bewildered population. The only SS casualty in Belgrade thus far was a private who had fallen and sprained his wrist. The Germans were amazed to find that no one attacked them in the city. The civilians went about their daily business as if nothing had happened. Klingenberg ordered Sergeant Hans Hossfelder to raise the German colors, replacing the Yugoslavian national flag with the German ensign shortly after 5 p.m. on April 12. Under Klingenberg's orders, his men began to strut about the city on patrol, giving the inhabitants the unmistakable impression that they were in charge.
The mayor of Belgrade came up to the Germans, complete with his entourage of city officials and in proper ceremonial dress. After asking what was going on, he inquired about the terms of surrender. Klingenberg told the mayor that his was the point team of several SS tank divisions, and if he did not check in with his unit by radio with the information requested, the Luftwaffe would continue their attempts to level the city. He also said that the air attacks would be followed by an artillery barrage and armored and infantry attacks that would spare no one.
The other Germans looked at their leader as if he was mad. Their radio was damaged and could not transmit, only receive; their unit was a considerable distance away; and they were out of ammunition and food. Sergeant Hossfelder later told his captain that he was in the wrong business, adding that the Propaganda Ministry could surely find a use for him.
The mayor fell for the ruse, and after an hour-long conversation with Klingenberg, he began the necessary arrangements for the surrender of the city. Then, as if on cue, a group of German aircraft flew over the city on a reconnaissance mission, and Klingenberg took advantage of the moment. He looked up, pointing to the sky, and reminded the mayor that the clock was ticking. Klingenberg gave his word that if all instructions were followed, no further harm would befall the city or its inhabitants. The city officials seemed relieved to hear that.
The soldiers and city militia agreed to lay down their arms in exchange for the Germans' ceasing additional attacks. The Yugoslav army stacked its arms in the city square, and Klingenberg had all of the men register with the mayor. Klingenberg then ordered the prisoners to quarter themselves in four of the largest hotels and posted a German guard to each building. The handful of Germans had just captured more than 1,300 troops and a city with a population of over 200,000 without firing a single shot. The city had suffered considerable damage, but not enough to prevent the locals from continuing with life and business as usual. Yugaslav soldiers outside the city, unaware of what had happened to their capital, drove into Belgrade only to be ordered by their superiors to lay down their arms, abandon their vehicles and march to the hotels. All the Yugoslavians complied without hesitation.
Klingenberg and his men made themselves comfortable in the city's finest hotel, making fake radio transmissions to reinforce the charade. They stockpiled bottles of wine and weapons, and two of the men disappeared with a couple of local women. Meanwhile, Klingenberg consolidated his position, knowing that things could still go wrong. If the main force did not arrive soon, the game was up. He had his men recruit locals to help procure every map, police record and tax record in the city.
The chief of police was ordered to provide a list of all criminals in the city, stating their crimes, age and other pertinent information. Women with nursing skills were to report for duty immediately, and all doctors were called in as well. Every liter of gasoline was accounted for, and oil, medical supplies and other necessities were placed in special holding facilities. The hospital was to be neutral ground, and all health care was to be maintained as a gesture of good will. Klingenberg even ordered the schools to remain open and placed no restrictions on daily business. He did, however, place an 8 p.m. curfew on the city; only citizens with a pass signed by him could legally venture outside their homes after that time.
The next day, April 13, more of Klingenberg's men who had remained on the opposite side of the river followed their leader into the city. Seeing the German flag, they believed that the main force had somehow bypassed them. They were amazed to find the "lost" men in command of the primary objective, with the locals not hostile but actually accommodating. Hossfelder told the new arrivals what had transpired and warned them to play along. They flexed their military muscle by commandeering every vehicle they could find.
Finally, on the night of April 13, the forward elements of Das Reich entered the city expecting a heavy fight. They had disregarded radio transmissions they had received telling of the city's surrender, believing it was an enemy hoax, possibly an attempt to lure German units into an ambush. Rumor had it that Klingenberg and his men had been captured, tortured and forced to release the codes required for proper radio communications. The XLV Corps commander was so furious at not having received his intelligence summary that he had threatened to have Klingenberg court-martialed if he were found alive as a prisoner. The first place he inquired for Klingenberg was at a brothel, figuring that he would find the renegade captain there. The corps commander's fury soon subsided when he learned why his junior company commander had been negligent in his duties.
The rest of Das Reich and supplemental army Panzergrenadierunits entered Belgrade in force the following day, and instead of fighting their way into the city, they were greeted with wine and cheese. The Yugoslav prisoners were conscripted to reinforce the German defense in case of partisan attacks. Sadly, when the mayor realized that he had been duped, he shot himself.
