Operation Rosebud was a ComStar plan enacted by Primus Myndo Waterly to sponsor the creation of the Free Rasalhague Republic, an independent state composed of the Draconis Combine's Rasalhague Military District, as well as worlds taken from the Combine by the Lyran Commonwealth during the Fourth Succession War.
Conceived in the aftermath of the Fourth Succession War, Waterly had several reasons for pursuing this plan. Unlike Primus Julian Tiepolo, Waterly believed that the more splintered the Inner Sphere became, the easier it would become for ComStar to push its agenda. Waterly was bitterly opposed to the Federated Commonwealth alliance, which she saw as a threat to a renewed Star League formed under ComStar. She recognized that by creating a buffer state between the Lyran-half of the Commonwealth and much of the Combine, it would free the Draconis Combine Mustered Soldiery to defend a significantly smaller border in any future war against Prince Hanse Davion. Waterly even believed that the creation of a new state might lead to the secession of the Isle of Skye, an event that would effectively sever the two halves of the new super-state. 
In mid-3030, with the Draconis Combine and the rest of the Inner Sphere still recovering from the conflict, Waterly brought her proposal to Coordinator Takashi Kurita and it was rejected out of hand.  Unperturbed, Waterly met with Takashi's Heir-designate, Gunji-no-Kanrei Theodore Kurita, on Dieron in September 3030. There, she made an offer.    
In return for releasing Rasalhague, the Combine would receive a large amount of equipment from their warehouses to help Theodore rebuild the DCMS. In addition, Theodore would receive ROM intelligence on enemy troop movements, preferrential rates on interstellar HPG transmissions, the transfer of the contracts of several mercenary units and finally the posting of ComGuard forces within Combine borders.   Theodore tentatively agreed.
Waterly then had to convince the First Circuit to accept the arrangement. She did so by assuring them that all mothballed Star League-era equipment would be stripped of lostech, the advanced military equipment used by the Star League Defense Force. She also claimed that the ComGuard troops would only serve to protect innocent civilians, and would not act as the aggressor. 
The Ronin War
For main article see: Ronin War
Matters proceeded well from there. The Kanrei turned a blind eye to the growing dissent festering in Rasalhague, while ComStar began to provide BattleMechs and other equipment to the Combine,  such as the Thorn,  the Sentinel,  the Crab,  the Kintaro,  and the Crockett (renamed the Katana by the DCMS).  These were all 'Mechs that had not been seen by the Successor States in centuries. They also provided more well-known designs such as the BattleMaster, some of which were still equipped with Star League era tech.  Unknown to virtually anyone, Precentor Dieron Sharilar Mori, secretly a Combine intelligence agent, arranged for a number of these 'Mechs to retain their advanced equipment. The DCMS, for its part, passed the matter off to a fortunate oversight by some anonymous ComStar clerk.
In 3034, the Draconis Combine formally recognized the creation of the Free Rasalhague Republic.  The Archon Katrina Steiner of the Lyran Commonwealth was likewise obligated to surrender the worlds they had taken from the Rasalhague District, despite the strenuous objections of Duke Selvin Kelswa III, leader of the Tamar Pact, among others.  Kuritan Warlords Marcus Kurita and Vasily Cherenkoff openly revolted against the move, triggering the Ronin Wars, with elements of the DCMS loyal to Marcus and Cherenkoff fighting against the nascent Republic KungsArmé and loyal DCMS elements under the command of the Kanrei. 
During this conflict, Waterly once again met with the Kanrei on Dieron. Waterly was infuriated that the Combine had retained twenty worlds from the old Rasalhague District, reorganizing them into the Alshain Military District. Theodore rebutted that the equipment House Kurita had received had been stripped of their advanced equipment. Both ultimately agreed to continue their arrangement, and Theodore further provided Waterly with a gift: Frederick Steiner, secretly held prisoner in the Combine for several years, would enter ComStar's service and be renamed Anastasius Focht, Precentor Martial of the ComGuard. Under his command and expertise, ComStar's military would reach impressive heights.   The Combine loyalists and the Free Rasalhague forces were ultimately successful, and the Free Rasalhague Republic would survive.
Matters in the Isle of Skye did result in a brief rebellion. It was quickly put down, though it pushed back Hanse Davion's plans for several years. Primus Waterly would secretly meet with Duke Ryan Steiner, laying the ground work for opposition to the Federated Commonwealth alliance for years to come. 
The greatest results of Operation Rosebud were made clear during the War of 3039. Facing new Kuritan formations using unknown machines severely demoralized the Armed Forces of the Federated Suns troops,  and House Kurita had an overwhelming advantage in the intelligence war, with ComStar ROM, the Internal Security Force and the Order of Five Pillars all working collectively to throw the strategic planning of the Davion high command into chaos. 
- Technical Readout: 3050 claims that an unnamed Precentor was responsible for the unauthorized release of several BLR-2C BattleMasters to the Combine, 'mechs which included the very advanced Cockpit Command Consoles. This unnamed Precentor was reduced to the rank of Acolyte, and was undergoing "re-education" on Terra as of 3051.  How these events fit with the actions of Sharilar Mori is unclear.
- ComStar (sourcebook) p. 59
- Heir to the Dragon (novel) p. 222
- Heir to the Dragon (novel) pp. 217-222
- Historical: War of 3039 p. 8
- 20 Year Update p. 64
- ComStar (sourcebook) pp. 59-60
- ComStar (sourcebook) p. 60
- Technical Readout: 3039 p. 240
- Technical Readout: 3050 p. 100
- Technical Readout: 3050 p. 118
- Technical Readout: 3050 p. 132
- Technical Readout: 3050 p. 194
- Technical Readout: 3050 p. 192
- Historical: Brush Wars p. 90
- Heir to the Dragon (novel) pp. 297-301
- Heir to the Dragon (novel) p. 349