Should I be proud of my Grandfathers military service?

Your friend is very misinformed as well as naieve. The United States Navy was a HUGE factor in World War II. They transported Soldiers and Marines to the beaches; Now, if they didn't do that, how would they have gotten to the shores of Omaha, Utah etc. The Navy also bombarded multiple targets during both campaigns (Europe and the Pacific) to lessen the resistance of opposing forces. A lot of ships came under attack from Japaneese Kamikazes, German Planes and German Uboats. The Navy basically won control over the water and helped to tighten the noose around Nazi Germany. You should be very proud of your Grandfather; he, like every other veteran during that time contributed to the war effort in one way or another.