According to this report:
At the time of my father's boyhood, the Haskalah movement had already commenced to penetrate the walls of the ultra-Orthodox Yeshiva where even the study of the Prophets were prohibited. My father often related how he and other students would keep the Tanach hidden within the Talmud volume from prying eyes of their teachers in order to study this literature clandestinely. To read Isaiah or Jeremiah with the Malbim commentarywas blasphemy.
"Students at the Yeshiva would forego many a meal, made available to them by generous families to whom serving meals to Yeshiva students was considered a great privilege or mitzva, to take special lessons in modern Hebrew and grammar from dedicated young men. This was particularly prohibited"
The statements seem odd considering the fact that R Yaakov Kamenetsky seems to have focused on learning T'nach and Grammar during his time at Slabodka. Although, there are reports of the Alter trying to prevent RYY Weinberg from learning Russian , and of controlling R Aharon Kotlers correspondence with his sister, i do not recall anything like what is described above. (The Alter himself had an interest in Haskalah at one point - see Benny Browns article on Slabodka.)