When Foyle arrives at the gate to visit the captain we see the registration of his car is AAP764. The guard lets him through, noting the registration number. We then see the car draw up to the house and the registration plate clearly shows the old faithful KVX757. (AAP764 is the registration of Foyle's car in the earlier series.)
When Taylor collapses at the dance the doctor helps him up. In the shot from behind Taylor's right arm is across the doctor's back, then the next shot shows Taylor's arm is in front of him.
The murder victim 'dies' noticeably differently between the initial scene and the flashback scene at the end, particularly in terms of the open/closed state of the eyes.
Captain Kieffer wears a Sam Browne belt, a leather belt with an attachment that goes over the right shoulder. Although its use has been called an anachronism because it was eliminated on officer uniforms issued from 1940, it was not officially abolished until June 7, 1942 when Change #22 to AR 600-35 was issued -- three months after the period depicted in "Invasion." Even then, a few officers continued to wear them. Also contrary to an earlier post, the lapel brass on Captain Kieffer's uniform IS correctly placed. Lapel brass was parallel with the the ground on U.S. Army officer uniforms during WW2.
The American soldiers are members of the 215th Engineering Battalion (Aviation) on a mission to construct an airfield for the U.S. Army Air Corps. However the members of this unit wear the divisional insignia of the First Infantry Division. The First Infantry Division did not have a unit like the 215th in its table of organization and, in any case, did not arrive in England until July 1942, four months after the events depicted in this episode.
The American officers and NCO's did not pack an extra outfit with them for their fly fishing outing on a Saturday. (L.L. Bean did not deliver to England during WWII) This was okay since the Army Corps of Engineers were usually expected to work on Saturdays. American military personnel during WWII disposed of all civilian clothing upon induction. Only military uniforms were to be worn until mustering out (demobbed). In addition, as Great Britain was a war zone wearing civilian clothing might be misconstrued as an attempt to desert, an implication not taken lightly. And with the various and many foreign military personnel in-country it may be misunderstood as an attempt at espionage. Additionally, the British citizens (at least a first ;-) were very welcoming of American military personnel and it was beneficial for them to identify themselves as such at all times.
In the Quotes section there is a exchange between Sam and Joe Fernetti. In the text he is identified as Pte Joe Fernetti. Pte is the abbreviation for the UK rank of Private. The U.S. Army uses the abbreviations of PVT (initial training period only) and PV2 for Private. However, Fernetti has a single stripe on his sleeve. He is a Private First Class (PFC), equivalent to a UK Lance Corporal.
No USAAF bases were built in the vicinity of Hastings during WW II; most were built in Norfolk. The land that is shown as the location of the airfield was unsuitable for a heavy bomber field in any case - it was hilly and crisscrossed by streams.
The dead girl not only has an obvious pulse, she is also visibly breathing.
The stockings Susan has been given by the American serviceman appear to be seamless, a post-war invention.
When Pvt. James Taylor is in the barn with Susan Davies, they hear a gunshot. He humorously tells her it was Farmer Giles and his blunderbuss. The reference is to JRR Tolkein's short story "Farmer Giles of Ham."
"Farmer Giles," although written in 1937, was not published anywhere until 1949, and would certainly not have been known to an American soldier until much later than that.
The registration numbers in each episode are anachronistic with figures preceding letters. Such plates were not issued until the mid 50s.
One of the American soldiers tells the English hosts his unit is from Fort Benning, Virginia. Fort Benning is actually in Georgia.
When interrogating the killer at the end, Foyle states that blood under the victim's fingernails match that of the killer, but there are several issues with this. Firstly, forensic science wasn't advanced enough at the time to prove this for a fact, and secondly, there was no sample from the killer to make a comparison with in the first place. It also beckons the question, if Foyle did indeed have the resources to establish this scientific proof, then why bother with all the other interrogations of all the other suspects prior to this point.
When Captain Kieffer initially tries to block Foyle's attempts to investigate the murder, he points out that the American base in technically American soil. This is incorrect, since the base is not an embassy or consulate.
On several occasions, military protocol was not followed by the American serviceman. In the real world, the behavior and disregard of basic regulations would have been dealt with severely. Some of the examples are, (1) the N.C.O.s did not salute the Captain on several occasions. (2) Foyle was invited by the Captain to speak to the NCO's regarding the local customs of the Brits. The sergeant spoke to Foyle with belligerence in a manner that would have caused embarrassment to his commanding officer.(3) When arriving into town, two privates were riding in the back of a jeep with the first sergeant driving and Captain in the front seat. The privates would have probably sent to the brig (stockade/guardhouse) for making lewd comments and whistling at a young lady who at the time was giving the Captain directions. (4) Private Farnetti asked the Captain for permission to go into town while his immediate superior, the sergeant was in the room at the time. (5) During the inquiry of Private Taylor regarding his whereabouts during the murder, the private sat behind a table while the Captain stood. Their positions regarding sitting and standing would have been reversed in a military circumstance.
James Taylor is a Pvt. yet claims he was "still in college" Christmas before last. That being the case it's odd he wasn't inducted as an officer; two years college would have been enough to qualify.