where did the name of the country originate from?
It is derived from the West Slavic tribe of Polans.
Poland
The origin of the name "Poland" derives from the West Slavic tribe of Polans ("Polanie"), who inhabited the Warta river basin of present-day Greater Poland region starting in the mid-6th century. 
who was helmut lent? A German night-fighter where was he born? Pyrehne, district of Landsberg an der Warthe, Province of Brandenburg, Germany name an educational institution that he attended. 2nd Air Warfare School did he participate in any invasions? Yes, the invasion of Poland.
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Poland [SEP] Etymology
The origin of the name "Poland" derives from the West Slavic tribe of Polans ("Polanie"), who inhabited the Warta river basin of present-day Greater Poland region starting in the mid-6th century. The origin of the name "Polanie" itself derives from the Proto-Slavic word "pole" (field). In some languages, such as Hungarian, Lithuanian, Persian and Turkish, the country's name is derived from the Lendians ("Lędzianie" or "Lachy"), who dwelled on the southeasternmost edge of present-day Lesser Poland, in the Cherven Grods between the 7th and 11th centuries — lands which were part of the territorial domain ruled over by the Polans.