need help with HW

i have alot of grammare mistakes could you please help me to fix tham?

In these chapters Billy is going to work in boathouse earlier. He is very exciting and he hopes that Mr. Bell will make early appearance. When Billy starts to work on HD-4, Casey explained to him why it's so important to keep project confidential. HD-4 was being developed for Royal Navy and its purpose was to attack and destroy the Germans' U-boats, or submarines. When Billy and Casey when to test HD-4. Something very strange happened there. Billy felt his self being thrown through the air and then he didn't remember anything. When he wakes up, he was in main house and nearly a dozen people. Mr. And Mrs. Bell and Mrs. McCauley-Brown hovered over top of him. Billy's doctor asked him "What happened there?" He told him that he was on HD-4 with Casey. Billy asked Mr. Bell what happened to Casey and HD-4 Bell told him that he didn't have enough time to exam HD-4.
I am wandering what really happened there. I think maybe this was an explosion of rocket from German submarines. I think what happened there, because Mr. Bell developing weapon to destroy German u-boats and submarines. German spy got information that Mr. Bell doing this and told to German government and they sent a rocket to his boathouse.