Only seen in the Voyager episode "Endgame", the Transphasic Torpedo is a powerful weapon from the future Federation, brought back by future Admiral Janeway. These weapons remain an almost complete mystery, except for the obvious fact that they do a very good job of destroying Borg Cubes. These cubes can be relatively easily destroyed through attacks to 'weak points', so this is the most conservative explanation for their effects.
Fans out to either inflate the power of the weapons or simply involve more baseless technobabble often make claims about the Transphasic Torpedoes. They claim that they 'phase' through targets - based on nothing but their name, and expressly contradicted by the episode in question which shows an impact explosion - and then construct elaborate 'explanations' as to why these weapons then disappear from Starfleet's inventory. An example of such invention is -
- Voyager was unable to transmit the data back to the Alpha Quadrant, so Starfleet HQ never put Transphasic Torpedoes into full fledged construction.
- As a slight variation on #1, the Transphasic Torpedoes were invented in a alternate future timeline, so the information would not have been available to starfleet HQ in the regular timeline.
- The materials needed to produce a Transphasic Torpedo are rare/expensive/not readily available in the Alpha Quadrant.
- The Transphasic Torpedoes were confiscated by Starfleet Temporal Investigations for whatever reason.
Some weaker explanations are:
- Transphasic Torpedoes only were able to pass through Borg shields because the Borg's shields function based on phase-adaptation, and thus Transphasic Torpedoes go right through them. (Note: this does not explain the hull-penetration).
- Transphasic Torpedoes are relatively unstable and cannot be stored for long periods of time, as they are likely to 'phase' out of existence. (No on-screen reference to Transphasic Torpedo instability)
As should be obvious, these are incredibly weak fan-justifications for something that is almost certainly not true in the first place. This is a fascinating insight into the mindset of science fiction fans in general, and Trekkies specifically.