Factual error: The film starts in the year 1936, and just like the RPG Indy uses to threaten Belloq with, the MP40s (or at the earliest, MP38s) are an arms-historical anachronism in this movie. As the numbers in their names imply, the MP38 was first produced in 1938. The weapons in the movie are not the similar-looking ERMA MP-36, you can see the ribbed, vertically angled magazine holders typical for the MP40 - its predecessors had either a 30°-canted, smooth magazine holder (MP36) or a round viewing port for checking the ammo (MP38). (01:31:45)
Factual error: The captain of the Bantu Wind, Katanga, wears a hat that originated from the Yugoslav People's Navy. But the Yugoslav Navy wasn't formed until 1945, 9 years after this movie takes place.
Factual error: During the fight scene at the German flying wing, the pilot ducks into the plane and pulls out a pistol and cocks it. The pistol is a P38 9mm semi-auto that the Germans did not issue until 1938, two years later.
Factual error: When Indiana Jones is fighting the big German by the airplane, the German punches Indiana Jones on his right cheek. Indy's face and body are both knocked down to the right, in the direction of the punch. When you watch this, you can see it's impossible to be knocked down in such a way. (01:17:55)
Factual error: Indy's satchel is a Mk VII gas mask bag, which was created for use in World War II, so it didn't even exist at the time the film takes place (1936). The similar Mk V existed at the time, though.
Factual error: When flying from Nepal to Egypt Indy passes over Arabia. The state of Jordan is shown, but in 1935 Jordan was called The Emirate of Transjordan.
Factual error: It should be a tricky task to put an object the size of the Ark on board a German VIIC submarine; perhaps you can find enough place inside but how do you manage to introduce that bulky case through the narrow hatches of the sub? Even the torpedo load hatches were just a little more than 21 inches in diameter.
Factual error: At the beginning of the movie, when Indiana is looking for the temple, you can hear a bird call. It also can be heard when Indy is running from the natives. The bird is a willow ptarmigan. It lives in very cold areas in the far north of North America. Even a very directionally-challenged ptarmigan could not possibly end up in South America. You can also hear the unmistakable laughing sounds of the kookaburras, only found in Australia.
Factual error: The German submarine that Indy stows away on has the number 26 on its side. The U-26 was a Type IA U-boat (it came into service in 1936 and was sunk in 1940), but the sub in the movie seems to be a Type VIIB or VIIC. It's true that the two types looked fairly similar, but they were different classes of U-boat.
Factual error: The interior of the German U-boat is completely different from the real interior of a Type VII U-boat, which is correctly shown in movies like 'Das Boot' or 'U-571'. For example, the ladder from the conning tower faces a different direction, the map table is too big and on the wrong side, the valves for submerging are on the side of the control room and not at its front and stern, depth gauges are too big...etc. All interiors were standardized, so it could not have been an individual build.
Factual error: When Indiana Jones ambushes the Nazis with the Ark, he threatens them with an anti-tank rocket. This is set in 1936, and anti-tank rockets weren't developed until the American M1 in 1942. The Germans immediately copied it from captured weapons and made their own much larger version known as the Panzerschreck, then Panzerfaust. The Russian RPG which Indy is holding was developed from the Panzerfaust in 1949. (00:41:55)
Factual error: Look to the right of the table lamp, there is a bottle of Myers Rum that has the modern plastic (silver/clear) cap and plastic pour spout. Not 1940s era. (01:33:10)
Factual error: When Marion is thrown into the pit of snakes and grabs the statue to prevent her fall, underneath her skirt she is wearing black spandex shorts. Shorts such as these did not exist in the 1930s time period of the film.
Factual error: The truck that turns over and blows up after Indy shoots the driver is a Mercedes Benz L701. It began production in 1944, and this movie is set in 1936, so the truck is not period correct. Also, the alleys are too narrow to allow this truck to turn a corner.
Factual error: During the travel to Nepal, "Thailand" is written on the map. The country has had this name only since 1939. This film takes place in 1936, when Thailand was called Siam. (00:23:20)
Factual error: At the beginning of the movie, Indy escapes in biplane with registration OB-CPO (a Star Wars nod, as noted in trivia). However the OB registration is used by Peru, and it should be followed by four digits, not by three letters. (00:12:10)
Factual error: When Indy flies to Nepal, there is a scene of the sea plane taking off with the Golden Gate Bridge in the background. The movie is set in 1936, and the bridge wasn't completed until 1937, with pictures from December 1936 showing large gaps still in the deck that do not appear in the movie. (00:23:00)
Factual error: Several times during the movie, Indy is under fire from Nazis or other bad guys wielding what look like MP-38 sub machine guns. The movie is set in 1936, 2 years before the weapon was even designed. The Erma EMP-36 has wooden parts (the grip), the muzzle spike at under the barrel is more pointy and the front sight are more massive than MP-38/40, and the magazine is tilting slightly forwards towards the muzzle. The MP-38/40 is all stamped sheet metal (no wood, because it would slow down production), the muzzle spike under the barrel is more smooth (maybe so it won't get stuck?) and the front sight is more simple (basically just a ring with rumble strips) than the ERMA's, and the magazine on the MP-38/40 is vertical.
Factual error: There's absolutely no way Sallah and Indy would be able to lift that 'lid' (for lack of a better word) off the ark. That thing is solid rock and would weigh close to a metric ton - and none of them look like professional deadlifters to me.
Factual error: When Indy is attempting to steal the Ark when driving the truck, one of the soldiers shoots him in the arm. Then another German punches him repeatedly in the same arm, causing Indy great pain and injury. After suffering a wound like that there's no way he'd be able to move that arm, let alone raise it above his head. But the next day after the boat is stopped by the sub, Indy jumps into the water and swims to the sub without any problems.
Answer: Indy and Marcus Brody believed that the Ark needed to be studied. They certainly didn't want to put it back where it was found. They believed that the U.S. government would find the best archaeologists, researchers, and scientists in the world to study the Ark. They are both upset that instead, the government has decided to simply lock the Ark away. This is why Indy says, "Fools. They don't know what they've got there," as he is leaving the building.
BaconIsMyBFF