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Concurrent:	Battle of Therum Battle of Feros Peak 15 Containment Breach
Next:	Skirmish on Casbin
Armstrong offensive Part of the Armstrong cluster campaign of the Eden Prime War
A map of geth offensive movements across the Armstrong sector for the duration of Operation: Window
Date:	17 June - 29 June 2183 CE (13 days)
Location:	Armstrong / Milky Way Galaxy
Outcome:	Operational SA victory Geth heretic forces capture all five systems of the Armstrong cluster Alliance forces expelled from the area Alliance launches "Operation Arrowhead" counteroffensive
Territorial changes:	Armstrong falls to geth heretic forces and the Saren's Alliance
Belligerents Systems Alliance Saren's Alliance Geth Heretics Commanders Abraham Mikhailovich Tyeson Mercier Sovereign Unit Y5552 Strength Systems Alliance Navy Fifth Fleet 13 Saratoga-class light cruisers SSV Saratoga 4 Geneva-class heavy cruisers SSV Tokyo 63 Mermaid-class corvettes 30 Warsaw-class light frigates 1 Nelson-class carrier SSV Nobunaga 90 SX3 Thunderbolt fighters 8 SX5 Yellowjacket interceptors Geth Heretic Army 11,200 geth troops 56 geth recon drones 141 geth assault drones 6,894 geth troopers 1,800 geth destroyers 1,024 geth juggernauts 940 geth hoppers 310 geth primes 26 geth armatures 9 geth colossi Geth Heretic Navy Heretic Reserve Fleet 1 geth dreadnought 5 geth battleship 26 geth heavy cruisers 10 geth light cruisers 23 geth heavy frigates 48 geth light frigates 200 geth strike fighters 130 geth dropships Casualties 21 ships destroyed, 8 damaged 2 ships destroyed, 5 damaged

"If the geth gain a foothold in the Armstrong cluster, they'll have a platform for launching raids across Alliance space...it could even be the forerunner of an invasion."

— Steven Hackett to Marcus Shepard emphasizing the danger of the geth attacks.

The Armstrong offensive, also known as the Geth incursions, Geth offensive, June offensive and, to Saren's forces as Operation Window, was a major Saren's Alliance offensive, carried out by the geth heretics, in the Armstrong cluster, with the goal of capturing all five of the cluster's systems using maneuver warfare. With geth forces bogged down pacifying the Feros colonists, a small strike force on Noveria and another geth force attempting to apprehend Liara T'Soni on Therum, Saren knew he could not hope to beat the Alliance military before their combined military might expelled his forces from the region and secured their borders. Operation: Window was the solution to this problem: a coordinated thrust into the Armstrong cluster, where all five systems would be captured, allowing for geth military installations to be established. Once that was done, the plan was to then invade the Batarian Hegemony from the east, Saren judging that with Sovereign committed to the assault, they could easily destroy the batarians, and perhaps even force them to join his alliance. With geth forces attacking from Hegemony space, the Alliance would be outflanked, and unable to properly respond.

The initial offensive was successful, with the geth seizing the Grissom system, and quickly expanding outward to capture the Gagarin, Hong, Tereshkova and Vamshi systems, establishing bases on Solcrum, Rayingri, Casbin, Antibaar and Maji respectively. Once the Alliance got wind of the offensive however, they immediately counterattacked, beginning an almost week long campaign to retake the cluster.