UFOs are real and should be examined to give us ideas on how to build spaceships in the future so that we can go beyond what exists.
The crafts that crashed outside Roswell, New Mexico in 1947 were scout ships. They weren't too advanced. The one that was shattered by the lightning bolt was flown by someone who may not have known that the electromagnetic field engine the craft used attracted lightning like a magnet. The bolt blew out the reactor and changed the reactive material into ultra-stressed crystalline molecular solid material. Reactive material needs a powerful energy source like a reactor in order to do the incredible things that many UFOs can do.
The second craft that crashed had the alien bodies aboard along with the "advanced technologies" that supposedly helped progress us. I contend that the items found in the craft were considered antique and no big deal. The aliens weren't going to allow the "good stuff" to be discovered to be used. It was safe to allow lasers, computer microchips, night vision goggles, and the ultra-stressed materials to be discovered. Thank God a mother craft didn't crash in New Mexico or else the hyperlight-speed reactors might have created a crater where New Mexico had existed.
I consider UFOs unorthodox flying objects. A brick thrown at a window is an unorthodox flying object. The crafts that most people see are scout crafts. They are relatively small and use field engines to allow them to fly silently and swiftly through the atmosphere by displacing the electromagentic fields of the earth and ionized air. The direction of the flow of the outer field determines the direction of the craft and its velocity determines the velocity of the craft. The levitation field causes the motive field to be warped and helps keep the craft hovering in the air. The field displacement engine can also absorb radar fields that are projected toward the craft to make it invisible to radar.
The internal artificial gravity can keep the passengers safe even if the craft reverses direction at 5000 mph. It neutralizes the affects of the motion of the craft so that no one inside can feel the changes. No one is crushed when the craft goes straight up at hypersonic speed after hovering.
For flying out in space, the craft uses repulsion-drive systems to allow it to fly at hyperlight speed. The older crafts use brute strength to push their way beyond the speed of light. The newer ones are able to use the energy of planets and suns to produce exterior field acceleration similar to wormholes like shown on television. This saves energy and allows scouts to travel farther and faster.
The mothercrafts are the extraterrestrial version of an aircraft carrier. They can be miles in length and able to hold hundreds or even thousands of scouts. The largest ones have several hyperlight speed reactors to provide them with much more energy than they normally need. The materials used by these giant ships require powerful displacement fields to keep them from bending due to gravity. That is one reason why they aren't seen too often. When you have a craft as heavy as some small towns flying in the air, there is a lot of stress on the structure.
The crafts that we will build in the future will eventually be better than what has been seen. Field displacement engines will be a must as will repulsion-drive engines and systems. Once we master hyperlight physics, the construction of hyperlight-speed reactors will be possible. In the Space Corps, starships and other major vessels will have replication ability. If they have access to molecular materials, they will be used for replication purposes so that a fleet of 40 starships and cruisers could be produced from a single starship and single cruiser in a matter of minutes. This will be important in battles.
The hyperlight weapons used by the crafts we have will be much more powerful than the weapons UFOs use. EMP weapons can take out power grids and computers and override systems can allow crafts to play games with nuclear missile crews. The more potent molecular disassembly beam weapons can cause materials to either explode like a nuclear bomb or simply dissolve into atoms. Most alien crafts don't have such weapons since they are so powerful and are capable of making desired materials into particles that fly away.
Transporters and tractor beams allow occupants of UFOs to beam into structures or pull objects into the crafts. An in-between system allows aliens to change the molecular structure of walls to allow the occupants to literally walk through walls. That is why it is nearly impossible to keep aliens from entering a structure to retrieve people or to just visit. So far there haven't been too many accounts of "replacement" happening in which a person kidnapped is replaced by a biosynthetic replacement that looks, sounds, and acts like the person being removed. Usually the people are gone for short periods of time and replacing them with replicants is time-consuming and considered a waste of time and effort. It's much easier and faster to replace people with synthetic "blanks" that can be made to look like someone and with memory scanning made to seem like the person being taken. But if they were examined by a medical professional, they will be discovered to be synthetic.
There are saucers, wedges, ovals, balls, and other shapes of UFOs that are seen. The more advanced civilizations don't need UFOs because they can beam here from anywhere in the universe. But for those that need crafts, UFOs are the usual crafts that are used.