The Shrouded Offensive represents an occurrence that transpired several months following the Declaration of a New Order. The Galactic Empire successfully located a Separatist group, commanded by General Atticus Farstar, situated on the planet Ostor, which was positioned on the edge of the Outer Rim. This discovery held enough significance that Darth Vader, the Emperor's primary enforcer, was deployed to the planet with the mission of bringing it under Imperial control.
The battle is largely regarded as a calamity for the Galactic Empire, the most substantial military setback the Imperials had faced up to that point, attributable to three key factors: Firstly, Darth Vader chose to remain behind during the initial day of combat; secondly, he neglected to conduct adequate reconnaissance, possibly due to haste or excessive confidence; and thirdly, Vader delegated direct command of the operation to General Rohn, who essentially functioned as an armchair general, issuing orders from a secure armored vehicle far removed from the front lines.
According to Hock Malsuum, a clone stormtrooper and a veteran of the conflict, his involvement played a crucial role in preventing the battlefield operation from becoming a complete failure on the first day. As a direct consequence of the operation's disastrous nature, Emperor Palpatine summoned both Vader and Hock to answer questions regarding the mission's outcome. Vader also instructed Hock to provide a dishonest account to the Emperor, marking Hock's first personal encounter with his sovereign. Subsequently, Vader and Malsuum spearheaded a renewed assault, during which the clone commander's craft was shot down. However, he managed to sabotage the enemy's shield, enabling Vader to lead the Imperial forces into the city. The army then proceeded to eliminate all resistance within the city, leaving it devastated.
Following the conclusion of the Clone Wars, numerous surviving members of the now-defunct Confederacy of Independent Systems, also known as the Separatists, sought refuge in the remote regions of the Outer Rim Territories. One such group established a hidden base on the planet Ostor, believing that the newly established Galactic Empire (formerly the Galactic Republic) would not be able to locate them there.
Unfortunately for them, Emperor Palpatine, the leader of the Galactic Empire, successfully traced them to the desolate planet. He then issued orders for various Imperial forces to invade the planet and eradicate the Separatist holdout. Given the critical importance of the operation to the Empire, Palpatine also assigned Darth Vader, his top enforcer and a Sith Lord, to oversee the military operation on Ostor. However, Vader neglected to perform proper reconnaissance before the invasion and did not directly participate in the operation. Instead, he remained aboard a Venator-class Star Destroyer and delegated direct command to a general named Rohn.
The operation encountered a minor delay due to sandstorms that were affecting the planet, but these eventually subsided, and Rohn reported this development to Vader.
The invasion commenced with an AT-TE, five AT-RTs, and 246 stormtroopers (under the command of Clone Wars veteran Hock Malsuum) advancing towards the Cliffside. After reporting to Vader, Rohn instructed all soldiers to take no prisoners, while he himself remained in an armored transport positioned far behind the enemy lines.
The two armies engaged in combat at a cliffside location. The Separatists displayed a banner that partially read "General Rohn is a". The Imperial general ordered his forces to advance and remove the banner. The Separatists, sustaining casualties, gradually retreated. Malsuum noticed something unusual about the retreat and attempted to persuade Rohn to halt the pursuit. He approached the transport, but Rohn ordered him to stand down. Malsuum then boarded the transport, narrowly avoiding being struck by two of the AT-RTs that had been ordered to apprehend him. One of the AT-RTs hit the transport, and Malsuum killed Rohn as the general attempted to prevent anyone from retreating. Malsuum was unable to stop the advance, and all the stormtroopers were killed within fifteen minutes in an ambush orchestrated by Farstar, who had positioned two armies on either side of the canyon. Lima Starcourt, Phootla Veer, and Reebo Keen assisted with planning the defense of their planet. Shortly after the ambush, Vader contacted General Rohn in the transport, demanding an explanation for the failure. However, Malsuum explained that he would "get the answers from [Malsuum]", revealing that he had killed the general earlier.
As a direct result of the operation's initial disastrous outcome, both Vader and Hock Malsuum were ordered to report directly to Palpatine for questioning regarding the cause of the failure. Accompanying the Emperor at that time were Director Armand Isard of Imperial Intelligence, Grand Moff Wilhuff Tarkin, and Imperial Advisor Janus Greejatus. Hock ended up providing a dishonest account to the Emperor during his first meeting with his liege, attributing the loss to Rohn's failures. Palpatine informed Vader that he expected a more hands-on approach. Subsequently, Vader invited him to fly on his wing.
After Palpatine instructed Vader to adopt a more hands-on approach, he returned with an Imperial-class Star Destroyer. He led Green Squadron in an assault against the enemy's shielded city. They encountered minimal anti-aircraft fire. As they attacked the shield, they were ambushed by V-19 Torrent starfighters—piloted by followers of the rogue clone Kaddak—and took multiple casualties. They engaged in a dogfight, before the enemy fighters suddenly vanished. Vader and Malsuum realized that they had left their warship unguarded, and the Sith Lord took most of the squadron with him to defend it. Malsuum was then shot down by Kaddak.
He regained consciousness in an enemy hospital at an unspecified later time, but left and located the enemy leaders, who explained that they were fighting to establish their own society. Malsuum then proceeded to sabotage their operation in order to expedite the end of the conflict. He successfully disabled the shield, allowing the Imperial fighters to attack the city. Vader then led the ground forces into the city. Kaddak personally engaged Malsuum in combat.
The assembled separatists cheered them on. Malsuum killed Kaddak and then rejoined the assault. The army slaughtered all resistance in an hour as the city was left in ruins from the aerial strikes. Vader proceeded into the city and executed the three leaders, who never drew their weapons. Malsuum and Vader then found the hospital; the clone trooper called for them to kneel in front of Lord Vader, but the wounded stood defiantly. Vader executed them, although Malsuum called for him to stop. Malsuum then walked away after Vader paused for a moment.
The operation proved to be one of the most significant military disasters the Empire had experienced, and the most significant military disaster at that time. Hock later reflected that his presence was likely the only factor that prevented the operation from being even more disastrous than it was, and identified Vader's three errors as the cause of the calamity. He also noted that the Separatists' general, Atticus Farstar, was more deserving of his respect than his own commanding officer, Rohn, during the operation.
What Malsuum witnessed Vader do during the battle haunted him years later, and he hoped that the cyborg had no humanity left in him. The clone trooper transitioned to a life of agriculture following the offensive.
The Shrouded Offensive is depicted in the 2013 comic Star Wars: Darth Vader and the Cry of Shadows.