The SR-71 Blackbird Astro-Nav System worked by tracking the stars
&gt; the flight plan was recorded on a punched tape that told the aircraft where to go, when to turn, and when to turn the sensors on and off.<p>This is equally fascinating to me. Before each flight, someone had to generate a flight plan and punch it onto a physical tape, then load it into the plan. T<p>No mid-flight &quot;re-calculating route&quot; if stuff goes wrong.<p>One of the most interesting and under-appreciated aspects of early aviation that is routinely forgotten by history is the fact that navigation was extremely difficult in a world before GPS. For example in WWII, pilots getting lost was a huge problem, especially for the Navy pilots. Imagine taking off of an aircraft carrier and flying hundreds of miles away from it, completing a mission and then trying to retrace your steps and find the 100 yard long dot in the wide open ocean again while flying at 10,000+ feet altitude. Pilots navigated with simple directions of, &quot;heading 310 for 50 knots, heading 120 for 80 knots&quot; and they would follow a handwritten piece of scrap paper and then try to come back. There were no landmarks to follow. To make things even more complicated, we didn&#x27;t exactly know distances very well. In a world like the ocean with no landmarks, you rely purely on compass and distances and time for directions. But if there is a tailwind vs a headwind then you could travel 80 knots in 30 mins instead of 45 minutes. This could put you wildly off course when you go to turn. It was incredibly scary to get into a cockpit and sail off into the ocean with no landmarks and hope to find a target and return back to the carrier (which itself is also moving). This is also why bombers and even long-range fighters actually had dedicated &quot;Navigators&quot; on board who&#x27;s sole job was navigation during flight.<p>As an example, The Battle of Midway was almost a complete failure for the USA because the main bomber squadron actually got lost trying to find the ships that they were meant to bomb. Iirc they had meandered around the destination area for almost an hour and were bingo on fuel. The squad commander had actually given the order to turn around and as the planes were turning around, one of the pilots spotted the Japanese carriers in the distance. The battle of midway up to this point was a complete failure and had overexposed the Navy. The first dive bomb attack had lost all but 3 dive bombers (one of which only survived because he got separated and lost). The Japanese were getting ready to counter strike on the remaining US Navy which were congregated (against the will of most admirals and generals) just a hundred miles away. The fighter wing had shown up before the second primary bomber wing (which had gotten lost) and had alerted the Japanese to the surprise attack, in addition to devestating losses (about 2&#x2F;3) for the fighters. If these lost bombers had returned back without completing their successful bombing raid, it is safe to say that history would be re-written. Japan would have destroyed the US Navy and eventually consumed the USA. This would have distracted the US from aiding Europe and Europe would have likely been lost to Germany. All because of how difficult it was to navigate before GPS.<p>I just find early aviation so fascinating with how they accomplished so much with so little. We often look back and forget so many simple things about aviation like navigation because we take it for granted today. Hell, my watch can pinpoint my location anywhere on earth to within a few feet. Yet location in the 40s and 50s was usually determined by drawing circles on a map that cover 50 mile diameters and saying &quot;we think we are somewhere in here&quot;.<p>A prime example is the original story. In a world before GPS, where we need precise long-range navigation, what are you going to do? You have to work with what you have. We didnt have satellites yet (well at least not ones like we needed), you are too high for anything visual on the ground, too fast to reliably navigate manually, so what&#x27;s left? The stars. I&#x27;m sure someone in that brainstorming meeting said it was impossible, but there were no other choices, so they figured it out. And it&#x27;s incredible!