My girlfriend and I were sitting on the beach, about 100 meters north of DanaBeach resort in Da Nang, Vietnam. We were sitting and talking for about 10 minutes or so when suddenly she saw something in the sky directly overhead that instantly caught her attention as strange. The time then was 6:45 PM. She mentioned immediately after the first sighting that she 'felt' something strange was happening above her, and she was compelled to look up.I looked up as well and my jaw instantly hung wide open, shocked and a bit scared at what I was seeing. It was a very large boomerang shaped craft moving at a steady speed and straight line to the north, towards Son Tra mountain. Instantly I could tell this was something strange, and my mind started racing to try and identify what this thing was. It didn't fit anything I've seen in the sky before. The object appeared extremely large, but it was also totally silent and had no lights whatsoever. My first reaction was that this thing was a kite someone had lost their grip on and was blowing over our heads. I quickly realized that this was no kite, because of it's shape and altitude. There were two layers of clouds that evening, one low marine layer type sporadic clouds, and one blanket cloud cover at a very high, upper atmosphere level that covered part of the sky, especially to the north. The object appeared below the top layer of clouds, but well above the bottom layer. The outline was clearly visible when contrasting the top layer of clouds. It had a perfect boomerang shape. When passing in front of stars, it blacked them out. The color was a greyish white and actually looked almost 'smoky' like it had some kind of 'active camoflauge'. It appeared to be a craft that was designed not to be seen.It maintained a steady, smooth speed as it passed overhead to the north and we lost sight of it as it blended in to the cloud cover towards the mountain. The sighting of the first craft lasted about 10 or 15 seconds. We were totally awestruck by this, and immediately started trying to figure out what it could have been. I was racking my brain trying to come up with some logical explanation but it just didn't fit anything I've ever seen in the sky. I've been in dozens of airplanes in my life, big and small, I'm a skydiver, I'm a climber with lots of experience with high altitudes and weird looking cloud formations. This was nothing I could explain, no matter how hard I tried. The shape was too perfect. It was at an altitude where there were no other clouds. Though it was similar in color, it contrasted to the clouds that were in the sky. It was moving too fast. It had no lights at all. If it were an airplane of some kind, it's relative size was too big. To look that big it would have to be flying at like 100 meters or something and would have been extremely loud. This thing was dead silent. The size, speed, perfect shape, altitude, lack of lights, clear straight line flight path... all of this didn't add up to any aircraft I've ever heard of. Da Nang has a pretty active airport, right near the beach where we were. There are both commercial and military planes and helicopters flying overhead commonly every day. We've seen all of these and are familiar with them. I should mention that the skies were busy with air traffic that night, which is normal. There were no planes that seemed to interact with the craft we saw, and they looked like the normal blinking lights that we see everyday.So that was the first one. We were pretty excited to have witnessed this, and a little shaken up by it too. We started talking about ufos etc. while looking straight up at the sky to see if anything else was there. After a few minutes of neck straining I thought nothing was coming. Every plane would catch our attention for a moment until we ruled it out as ordinary. It was looking at one of these planes that my eye caught the second boomerang craft. I could not believe I was lucky enough to be seeing this again. We got a longer look at this one, maybe 20 seconds or so before it blended in to the clouds to the north. It looked exactly like the first one and had the exact same flight path. I checked the time after we saw it, and it came about 15 minutes after the first one, at 7:00PM on the dot. We were basically dumbfounded at this point. And sat waiting and watching for anything else that might appear. Nothing came. It is the next day as I write this, and I'm pretty blown away by what I witnessed last night.I hope somebody else saw this besides my girlfriend and I.