In The Name of Allaah, The Most Merciful, The Bestower of Mercy.
Imaam As-Sadi [may Allaah have mercy upon him] said: Allaah commanded (the believers) – in several verses of the Qur’aan – to perform Jihaad (see footnote a), prepare as much strength as possible against the enemies and to be cautious of them. This cannot be accomplished except by learning the arts of war and the crafts on which this strength and caution depends.
Commentary: Allaah said: [وَأَعِدُّواْ لَهُم مَّا ٱسۡتَطَعۡتُم مِّن قُوَّةٍ۬ – And make ready against them all you can of power- (Surah Al-Anfaal. Aayah 60)]. This cannot be accomplished except through knowledge. (see footnote b) 
Footnote a: Salafi Shaikh Fawzaan on Jihad in our times and the guidelines of Jihad according to Islam: https://abukhadeejah.com/salafi-shaikh-fawzaan-on-jihaad-in-our-times-and-the-guidelines-of-jihaad-according-to-islam/
Footnote b: Imaam As-Sadi [may Allaah have mercy upon him] said: Allaah [The Exalted] said: Allāh [The Most High] said:
لَقَدۡ أَرۡسَلۡنَا رُسُلَنَا بِٱلۡبَيِّنَـٰتِ وَأَنزَلۡنَا مَعَهُمُ ٱلۡكِتَـٰبَ وَٱلۡمِيزَانَ لِيَقُومَ ٱلنَّاسُ بِٱلۡقِسۡطِۖ وَأَنزَلۡنَا ٱلۡحَدِيدَ فِيهِ بَأۡسٌ۬ شَدِيدٌ۬ وَمَنَـٰفِعُ لِلنَّاسِ وَلِيَعۡلَمَ ٱللَّهُ مَن يَنصُرُهُ ۥ وَرُسُلَهُ ۥ بِٱلۡغَيۡبِۚ إِنَّ ٱللَّهَ قَوِىٌّ عَزِيزٌ۬
Indeed We have sent Our Messengers with clear proofs, and revealed with them the Scripture and the Balance (justice) that mankind may keep up justice. And We brought forth iron wherein is mighty power (in matters of war), as well as many benefits for mankind, that Allah may test who it is that will help Him (His religion), and His Messengers in the unseen. Verily, Allah is All-Strong, All-Mighty. [Surah Al-Hadeed. Verse 25]
Allāh [The Most High] informs us that He sent the Messengers to guide the creation [i.e. humankind and Jinn] and supported them with clear proofs that clearly manifest the realities, demonstrated the truthfulness of the Messengers and the reality of that which they brought. He revealed to them the Scripture wherein there is guidance and mercy, and revealed to them the Balance, which is justice, and by way of which justice, its foundation and subsidiary branches are known, and so that humankind may keep up justice when they act upon it in their beliefs, manners, deeds, behaviour and in all their affairs. Therfore, all their affairs and circumstances will be established upon righteousness and steadfastness when they act upon that which Allāh revealed in the Scripture and the Balance.
And Allāh [The Most High] informs us that He sent down iron wherein there is mighty power (in matters of war) as well as many benefits for humankind, and He specifically mentioned its benefits in matters of war and then generalized it in all other matters. Allāh sent down iron for the (purpose) of these beneficial, indispensable matters and affairs that bring about perfection – in specific and in general. All things – except a few – are in need of iron. Indeed, Allāh mentioned it in the context of the favours He has bestowed on the servants, and this necessitates that these benefits are extracted through every way- necessitates education in military expertise and affairs of war, manufacture of weapons and its accessories, maritime transport, land transportation, aircrafts and other things that benefit the servants in their religious and worldly affairs, just as Allāh [The Most High] said:
[ وَأ عدوا لهم ما استطعتم من قوة ومن رباط الخيل ترهبون به عدو هللا وعدوكم- And make ready against them all you can of power, including steeds of war (tanks, planes, missiles, artillery, etc.) to threaten the enemy of Allah and your enemy]. [Surah Al-Anfaal. Aayah 60]
Allāh said: [حذركم وخذوا – Take every precaution for yourselves]. [Surah An-Nisaa 102]
This addresses the affair of preparing all that is possible of power – mentally, politically, materially and religiously, and taking every precaution against the enemies through every means and way. All the small crafts and big ones, the inventions and defense [fortifications] are included in this generality. Therefore, this Islamic religion urges towards sound progress and strength in all respects contrary to what its enemies fabricate that it is impotent, remiss and threadbare. They (i.e. the materialists) know their lies and slander regarding it; however self-importance and arrogance became convenient for them. And out of their ignorance, they think that they have decorated their speech and made it vague so that the sensible people will not know its meaning, although every sensible person knows their lies and slander; rather only the ignorant and misguided are deceived by them – those who do not know about Islam- neither a little nor a lot; but these enemies portray an evil image of Islaam to them in order to decorate that which they utter of falsehood. Otherwise, whoever knows Islam with a sound acquaintance, he knows that indeed the religious and worldly affairs of humans cannot be established in an upright manner except through it, and that its wise teachings are the greatest proof regarding the fact that it is a revelation from the All-Wise, Worthy of all praise (Allāh); The Knower of all the Unseen and The Seen, Merciful to His servants and hence ordained this religion for them…
Also read: Some Causes of Weakness In The Ummah- By Imaam Abdul Azeez Bin Baaz:
Ref 1: From 27mins 58secs to 28mins 32secs. https://www.al-badr.net/detail/3KwCnaB5tN