Has the State Alchemist pocket watch ever been shown to be of use in a transmutation?

Question

In the beginning of the series (both 2003 and Brotherhood) Cornello takes way Ed's pocket watch in order to prevent his circle-free transmutation (which is later revealed to be pointless). From this, it was implied that the pocket watch has some sort of effect on a State Alchemist's transmutations. I seem to also recall that in the 2003 series, when Ed became a State Alchemist and was given his watch, he was told it could boost his alchemy.

However I don't recall any instance in either series where this was the case. It's not used as a mobile circle as each combat State Alchemist had their Transmutation Circle with them (Roy's ignition gloves, Gran's gauntlets, Armstrong's metal knuckles, Kimberly's own hands) and Shou Tucker was never shown to use his (and I doubt that he used it for producing the Alexanina Chimera because he was capable of doing this from the start, having done a similar transmutation before becoming a State Alchemist).

I recall at one stage the chain was used to bind someone, but what I would like to know is if there was any situation, in either series, in which the boosting capabilities of the State Alchemist pocket watch is shown to have benefited an Alchemist's transmutation (without the addition of Red Stones/Fake Philosopher Stones as per the Lior Rebellion in the 2003 series).

Answer 1

It is somewhat difficult to answer this with complete certainty without analysing every single transmutation that appears in Fullmetal Alchemist. However, I will give an answer based on my memory and impressions of the series.

In the manga-based continuity, the watch appears to serve largely as a marker of identity; there is never any comment about the watch's powers. We never see the watch invoked or made reference to as a source of power when State Alchemists transmute substances.

I do not know the 2003 series as well, but my impression is that while the claim that the watch amplifies transmutations is reasonable, we are never actually shown an instance where it is explicitly used in a transmutation. It is entirely possible that the State Alchemists we see are drawing from the watch's power anyway, when they attempt transmutations, but we do not ever directly see it.

The current revision of the FMA Wikia appears to support my conclusion:

Although the manga does not describe the pocketwatch as anything more than official proof that the carrier is a State Alchemist, the 2003 anime suggests that each pocketwatch is an alchemical amplifier. The 2003 anime also depicts the watch's silver chain as extendable, as in the instance when the Strong Arm Alchemist, Major Alex Louis Armstrong uses it to tie up a target.

In particular, were there actually an instance where the watch is explicitly used, I would expect there to be a note of it here, seeing how rare such an instance would be in the course of the anime.

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Skimming over the early Lior arc in the manga, incidentally, I cannot find any instance where Cornello takes Edward's watch from him. The watch also does not appear in this part. (I was only able to tell that Edward had his watch because I could see the chain.) This also does not occur in FMA:B.

As might be expected then, the section of the Lior arc in the 2003 anime where Cornello takes Edward's watch is not in the manga-continuity. (This is after Ed and Al have escaped from the fight. Cornello turns a mob on them, and they are captured again. The watch is then taken.)