The Creature of fort 13

The story I am about to tell you will stretch the limits of your imagination, and cause you to call me a liar, I do not doubt that some of you will. Before I start however I would ask that my sanity not be questioned due to the fact that even I cannot provide an answer.  I am only able to answer the question of what happened in hope that others might be spared.
    It had been eighteen months since the invasion of my homeland, the enemy had taken the capitol in just three months; now all that remained was the resistance.  We tried to remove the invaders but failed, for we were not trained at the skillful art of combat; we were farmers and hunters who had brought whatever weapons we had at home.  They had pushed us to the border of our country to a collection of lakes of such a depth and size that someone seeing them for the first time would confuse them for the ocean, they were indeed extravagant.  Within these lakes sat a multitude of islands; some were large enough to hold entire airfields while others were only large enough to hold a moderate fortification. 
It was on one of these smaller islands--where I worked as a radio operator-- that I lived.  It was currently my turn to walk patrol around the wall.  There were five walls that were one meter in thickness and three meters in height; the only door was in the center of the southwest wall and was the same thickness as the walls on either side of it.  Towards the end of my patrol I felt compelled to check the time on my watch and I saw that it was five minutes to midnight.  Upon seeing this I started to walk to the main building that housed the radio room, the command center, and the officers quarters; as I reached the doors of the building I once again checked the time on my watch and saw the hand tick away the last few seconds until midnight. 
Upon reaching the twelve the second hand and all other movement of the watch ceased.  Thinking nothing of this except that I had to rewind my watch I once again turned to enter the building; but before I was able to take two steps I heard the alarm sound signaling that we were being attacked--this surprised no one because we had not been attacked in a fortnight and anticipated an attack--at once I started to run to my radio to alert the other islands and to ask for support.  Upon reaching my radio I discovered that I was unable to broadcast, what surprised me even more was the fact that I could receive signals with extreme clarity but I was incapable of transmitting.  Feeling safe inside the walls of the fort I hastily moved to insure that the radio was connected to the antenna.
Upon reaching to outermost doors of the building I heard the most ghastly sound that had ever reached my ears, a sound so horrendous that I almost thought I had imagined it.  I knew however that my mind was not the cause of the sound; turning, I saw that the sound which had horrified me had come from a man who had had his intestines torn from his still living body.  But then when I saw what had killed this man I was confronted by a sight that terrified me more than the man's scream, a being so gruesome that I was certain it had come from Hell itself.  The being I now saw had the head of a bat, the torso of a man, and the legs of a horse. For reasons I do not know I tried to shoot the beast but to my bewilderment the bullets seemed to have no effect on the creature except to further enrage it.  I, being the genius I am, stood my ground as the beast turned towards me and to my astonishment grew wings of a bat and flew at me.  I choose this moment to run for the building--which I safely entered--and barricade myself inside the radio room. 
After securing the door I grabbed the crucifix from above my bed to ward off the demon.  As I sat huddled in the corner clutching the crucifix with all my might I saw the beast approach the door through the translucent window.  When it reached the door I saw it pause for what felt like hours, then it moved on.  For some unknown reason I choose this time to wind my watch, and looking at the clock to see the time I was amazed to find that that clock had also stopped; looking back at my watch I was mystified to see that even after winding the watch was still stopped.
Thinking that the beast had gone I decided that I would try to escape the island.  Moving from my room I made my way down the winding corridors to the doors that lead outside; I then made my way to the door in the wall which to my surprise was undisturbed,--I also noticed that a perfect pentagon had been burned in the grass connecting the five corners of the compound--all this time I had  not encountered the monster.  Opening the door I made my way to the beach where we kept some boats incase we had to leave the island.  I was shocked to find that all of them were shredded to the point that I could not tell that they were boats.
At once I felt a chill that caused the hairs on the back of stand straight up on end.  I turned around to see the beast standing not five feet from me!  What happened next I still do not believe, the beast opened its mouth and said, "hac nocte animam tuam desinit", and then the beast brought back its hand and with one swooping motion sliced my neck! 
Now we, the dead, walk the island and keep a watch for invaders; by day we are allowed to inhabit our bodies and interact with the living but we cannot leave the island lest we face punishment at the hand of the demon, at night our spirits leave our bodies and we travel to the other islands to recruit others to our group.  We never regained our homeland but the enemy has never tried to step foot on these islands for they fear the stories of what has happened here.