SureFires, unless specifically stated on the specific individual packaging, specs sheet or manual, are rated "weather proof". X200/X300 are rated waterproof to 20 metres as standard I believe.
However, and this is where it gets complicated, Most classic (standard body) SureFires are capable of being tested and rated waterproof by SureFire on an individual basis as waterproof to 33 metres (which is depth required by the US Navy specifications). Tested individual lights with have the suffix "N" such as 6PN.
Modern products, such as those that use the two-stage push button pressure switch are less likely to handle being submerged due to wear-through-use that the o-ring is seeing due to the increased number of rotations etc these TailCaps see.
Clickie TailCaps that see hardly any rotation are the ones most likely to maintain good o-ring seal.
SureFires are designed to handle being flooded (and as long as washed through with pure water to remove any salts/deposits etc) should be able to recover from being flooded after being slowly dried.
Bottom line:
SureFire does not make divelights. Most will handle an occasional dunking.
Some SureFires can lead good lives as divelights but the user has the primary responsibility for ensuring the seals are kept in good order and sufficiently lubricated etc.
Whether your individual SureFire is waterproof is something you can find out for yourself and will be responsible for maintaining if you so wish.
I hope this helps?
