In Germany and some other European countries, this series was dubbed in an unconventional way, using very funny, often absurd expressions and phrases. Because of that, it became very popular (unlike the English version) and is still regularly repeated on German TV today.
The most ubiquitous firearm used in the series is a Model 1934 Beretta in 7.65 Browning (aka .32 ACP). It appears in almost every episode involving a handgun. When a revolver shows up, it is almost always a Colt Detective Special.
According to the DVD commentary, neither Roger Moore, an uncredited co-producer, nor Robert S. Baker, the credited producer, ever had a contract other than a handshake with Lew Grade. They produced the entire 24 episodes without a single written word guaranteeing that they would ever be paid.
Throughout the series, Tony Curtis' character Danny Wilde is almost always seen wearing gloves. According to DVD commentary, this was a gimmick developed by Curtis to make his character unusual, and therefore create some buzz for the series.
Popular in Denmark and still repeated on TV 40 years after. The Danish title "De uheldige helte" (The Unlucky Heroes) plays with the words held=luck and helt=hero. The title tune was also a bit of a hit.