In my view, and knowing at least this much about the encounter, it sounds to me like the pilot intended it.
They could have phased the craft much earlier and left the area and the patrol boat would have been none the wiser.
Instead the pilot (for reasons unknown) decided to execute a strategy which indicates they wanted to be observed, likely shot at, and then use that as an excuse to send the ammunition back to the patrol boat. So in my mind, and with what little we do know, it sounds like the ET person inside took a more things down a more aggressive scenario than explicitly necessary (avoidance was the other obvious option).
That thought crossed my mind. It would be strange if the pilot did otherwise.
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One thing to keep in mind (and treat this as hear say) is that the "energy screen" (as you nick name it) in a normal flight configuration is designed to absorb ambient energy that...despite all deflection techniques...still makes it inside the field system.
In otherwords, the outer field trap is for capturing random particles and energy that makes it in. 99% should not in a normal configuration. (Note, certain flight modes have configurations which increase the absorption for specific intents)
So the energy/particles that makes it into the trap, is by and large normally deflected. Depending on the stealth and flight configuration that can be increased. In this case, it seems the ET piloting said craft were altering the intended purpose of the outer fields surrounding the UFO to cause them to redirect the ammunition and all the energy behind them in a new direction.
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For people who read this in the future, in case you don't understand what I am trying to say:
Imagine if you made a post card sized field-generator from ET technology, one that created a torus-like field. Like the one depicted at the 1 minute mark in this video I just found:
https://www.youtube.com/watch?v=EKtevjrZOGs
If you put this post card sized field-generator inside a heavy metal container, when you turned this field generator on in a field with sunshine, it would turn completely black. After a minute or so if the field generator were to turn off, you would notice an immense release of heat and light energy. When you ran up to the metal container, you should notice that it looks like it has been seared by heat.
Congratulations, you have made the first of many components that goes into ET crafts. This stamp sized field-generator generates a torus-like field that absorbs ambient energy. Rather than it reflecting light and heat, (and radiation) it captures it like a spacetime [heat]sink.
If you leave it on for hours, the next time you'd turn off the field, you would see a burnt field from the immense release of focused energy being captured in the sink.
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What if, you designed a more complicated system, one which could dynamically redirect and compress this heat and energy _around_ the metal container? Congratulations, you win a nobel prize, you just learned how to ~violate/bypass~ a few laws of physics. You've just circumvented friction and various interactions of thermodynamics to a certain degree.
Now if you add a UFO (the generator itself) in the center with the capability to generate inner layers of "phased space", you are 5/10ths of the way to a full ET craft. As a bonus you now can operate a craft/generator which is no longer fully registering as a conventional space-time object. Your field generator has now become an integral part of a spacecraft. Which is at times, is neither here nor there in the conventional sense.
The fields can be reconfigured for different purposes if the pilot wanted to do that. For example the pilot could distort the rate of time, but it would mostly be from fields beneath the energy screen. Yes, allegedly the ET can distort the shape of the various layers to create pronounced side-effects.
Anything is plausible, though unless the outer side was fully discharged, i'd find it hard to believe the missile would last 24 seconds. Stranger things are possible I guess.
The real meat and bones in the case of the missile would be to see what kind of abnormal stresses the missile had been exposed to. Though, considering missiles are designed to penetrate and explode, that would probably be nearly impossible to determine.
You are correct, it is entirely within the realm of possibility.
The fact that you can consider such a possibility is likely to stick out in someones mind. Hope I don't get in trouble for that.
They should have figured this out pretty quickly. The big question is why did it take this many encounters for them to call off these efforts.
Also, what I exposed to you, should also eventually bring up the question:
Well, if (some) ET crafts use technology like what Fore has described, what could shoot down one of these things?
What would it take to bring down an ET craft?
(Probably should review cases of [allegedly] downed ET craft and figure out what they have in common. Could you really tell genuine ET craft from ones made on Earth by the lack of a specific feature set? What technologies do reverse engineered craft lack that the authentic ones have? Your mind is a database, so you (and anyone else reading) should start sifting and see if you notice anything.)