This was something I always wondered, but never saw mentioned before. First there was this apparent Red Herring from Cortana in Halo 2: [url]http://youtu.be/Lj8OUqki47I?t=7m28s[/url] And then this Terminal in Halo 3: [quote] [00:H 19:M 02:S] The seventh and final wave of container ships, barges, tankers and military vessels engage my fleet; another 214,320 ships, many in excess of [50,000 tonnes], engage my seemingly disrupted vanguard. I continue to fight just well enough to seem lucky. [b]Mendicant, or the enemy, has been sending a small percentage of its fleet elsewhere. Good. Let them believe they can seize a foothold somewhere inside the sphere.[/b] [/quote] Now when Mendicant Bias communicates with The Flood in the Terminals, the Gravemind is marked as LF.Xx.3273. Look at the stamps for the transmissions about "Cold Storage." [quote] "REPORT: CONTAINMENT FAILURE LF.Xx.3273 research and containment facility; [delta site] has experienced catastrophic specimen containment failure. All apertures into facility will be locked until further notice. Atmosphere evacuation and [reduction of ambient temperature] protocols have already been enacted. Request maintenance and security detail [at earliest opportunity]. [8 minutes] elapsed since initial containment failure. [/quote] The dates given in the rest of the logs correspond to a time shortly after the firing of the Halos, so this outbreak happened quickly. It is also worth noting that 2401 was [I]immediately[/I] unresponsive, so the single pure form that broke free being the source of the Gravemind seems unlikely. It also seems unlikely that 2401 went Rampant so early. Finally, the logs also suggest that the creature escaped via slipstream, which is likely the teleportation grid that the monitors (and Gravemind via them) have access to. Given this information, I suggest that the lake on Delta Halo is in fact a crater left by the original Gravemind's ship, which hid beneath Delta Halo to avoid the Rings, and then promptly took over the installation and waited.