Re: The Doomsday Machine - why no photon torpodoes?
So Decker may have had an unrealistic hope that phasers might have more of a chance than a torpedo, which is why he didn't launch any from Enterprise.
Or he wanted to use the phasers as cutting beams to open up a section of the planet killer's hull and keep the torpedos in reserve to then target such an unexposed area.
"The first duty of every Starfleet officer is to the truth, whether it's scientific truth or historical truth or personal truth! It is the guiding principle on which Starfleet is based! Jean-Luc Picard