Militants assaulted and gained entry to Pakistani Naval Station Mehran, a naval air station in Karachi, Pakistan, on May 22. The situation is rapidly evolving and ongoing, with Pakistani military commandos reportedly on the scene and working to clear the facility. The fighting is now in its fourth hour. As many as 22 militants are reportedly involved in the assault. Six have been reported dead, four have been captured, and 10 to 12 more are still fighting. Nine explosions have been reported, including one described as "massive" (there are reportedly ammunition as well as fuel depots at the facility). Initial reports suggest that at least four people at the facility have been killed and five wounded, but these figures are likely to rise as the situation evolves and more information becomes available. Fighting took place in or near three aircraft hangers housing Pakistani P-3C Orion maritime patrol aircraft. These aircraft are surplus U.S. Navy airframes that have been delivered since 2007, and there are reportedly U.S. nationals serving as contractor personnel that work at the facility in connection with them. Casualties among these Americans have been reported. One of these aircraft reportedly has been destroyed, and another may have been damaged. The attack is a complex and sustained assault, and it is the first of its kind in Karachi, a valuable port city in Pakistan. Though attacks have taken place here before, this attack is of a new magnitude and variety entirely. While organized criminal elements define the political and security landscape in the city, this sort of attack — not to mention the target of the attack — is more akin to those of Islamist Pakistani Taliban groups. Notably, this is a guarded military facility. While there may have indeed been weaknesses in the security (one report has suggested that the militants gained access to the facility from an adjacent military museum, while another reported indicated a sewage pipe was used to gain entry), an attack of this scale and on a facility such as this raises significant questions about an inside job. Indeed, the possibility that security personnel were compromised and facilitated the entry of the assailants into the facility cannot yet be ruled out. Attacks are an inherent danger in Pakistan, where sympathy for and undercurrents of Islamism are felt broadly — increasingly even among elements in Punjabi areas in the south and east. But it is also noteworthy because assailing a defended facility requires significant effort and can require the assaulting force to expend much of its fighting strength, explosives and ammunition on simply breaching the perimeter. If they either found a weakness in the perimeter, or were allowed to slip through it, they would enter as a more fully equipped and coherent force, capable of inflicting more damage and destruction as Pakistan mounts its response.